License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-01 15:07:57 +01:00
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2013-10-04 10:24:49 +02:00
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2005-04-16 15:20:36 -07:00
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2017-02-02 17:54:15 +01:00
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2005-04-16 15:20:36 -07:00
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2017-06-20 12:06:13 +02:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2017-06-20 12:06:13 +02:00
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2014-09-24 10:18:47 +02:00
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2023-10-10 04:58:29 +01:00
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2014-09-24 10:18:47 +02:00
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2017-06-20 12:06:13 +02:00
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2013-10-04 10:24:49 +02:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2013-10-04 10:24:49 +02:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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2005-11-07 00:59:43 -08:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2021-06-01 17:11:20 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2009-08-10 12:33:05 +01:00
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2017-03-05 12:07:33 +01:00
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2009-08-10 12:33:05 +01:00
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2005-04-16 15:20:36 -07:00
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2006-10-29 22:46:36 -08:00
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2017-03-05 11:10:18 +01:00
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2006-10-29 22:46:36 -08:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2013-10-04 10:24:49 +02:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 11:10:18 +01:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 11:10:18 +01:00
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2019-04-09 10:43:57 +10:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 12:07:33 +01:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 12:07:33 +01:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 12:07:33 +01:00
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2015-10-23 14:32:34 +02:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2019-07-16 16:19:25 -04:00
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2015-11-26 13:55:39 +08:00
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2017-03-05 12:07:33 +01:00
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2015-11-26 13:55:39 +08:00
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2017-03-05 12:07:33 +01:00
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2015-11-26 13:55:39 +08:00
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2017-03-05 11:10:18 +01:00
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2015-11-26 13:55:39 +08:00
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2017-03-05 11:10:18 +01:00
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2015-11-26 13:55:39 +08:00
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2017-03-05 11:10:18 +01:00
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2020-10-27 14:39:43 +00:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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2020-10-27 14:39:43 +00:00
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2005-04-16 15:20:36 -07:00
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2013-10-04 10:24:49 +02:00
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2017-03-05 11:10:18 +01:00
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2010-05-07 14:33:26 +08:00
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2017-03-05 10:33:16 +01:00
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2017-03-05 11:10:18 +01:00
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2010-05-07 14:33:26 +08:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2013-10-04 10:24:49 +02:00
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2017-03-05 11:10:18 +01:00
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2010-05-07 14:33:26 +08:00
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2017-03-05 10:33:16 +01:00
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2017-03-05 11:10:18 +01:00
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2010-05-07 14:33:26 +08:00
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2013-10-04 10:24:49 +02:00
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2017-03-05 11:10:18 +01:00
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2005-04-16 15:20:36 -07:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2022-11-15 17:45:52 -05:00
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2023-03-07 23:31:58 -08:00
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2017-03-05 11:10:18 +01:00
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2019-10-16 15:13:41 +01:00
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2019-09-24 16:07:45 +01:00
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2017-03-05 11:10:18 +01:00
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2019-10-16 15:13:41 +01:00
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wait: add wake_up_pollfree()
Several ->poll() implementations are special in that they use a
waitqueue whose lifetime is the current task, rather than the struct
file as is normally the case. This is okay for blocking polls, since a
blocking poll occurs within one task; however, non-blocking polls
require another solution. This solution is for the queue to be cleared
before it is freed, using 'wake_up_poll(wq, EPOLLHUP | POLLFREE);'.
However, that has a bug: wake_up_poll() calls __wake_up() with
nr_exclusive=1. Therefore, if there are multiple "exclusive" waiters,
and the wakeup function for the first one returns a positive value, only
that one will be called. That's *not* what's needed for POLLFREE;
POLLFREE is special in that it really needs to wake up everyone.
Considering the three non-blocking poll systems:
- io_uring poll doesn't handle POLLFREE at all, so it is broken anyway.
- aio poll is unaffected, since it doesn't support exclusive waits.
However, that's fragile, as someone could add this feature later.
- epoll doesn't appear to be broken by this, since its wakeup function
returns 0 when it sees POLLFREE. But this is fragile.
Although there is a workaround (see epoll), it's better to define a
function which always sends POLLFREE to all waiters. Add such a
function. Also make it verify that the queue really becomes empty after
all waiters have been woken up.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211209010455.42744-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2021-12-08 17:04:51 -08:00
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2005-04-16 15:20:36 -07:00
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2007-12-06 17:34:36 -05:00
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2011-12-01 00:04:00 +01:00
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2007-12-06 17:34:36 -05:00
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2005-04-16 15:20:36 -07:00
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2019-10-16 15:13:41 +01:00
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2005-04-16 15:20:36 -07:00
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lockdep: annotate epoll
On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote:
> I remember I talked with Arjan about this time ago. Basically, since 1)
> you can drop an epoll fd inside another epoll fd 2) callback-based wakeups
> are used, you can see a wake_up() from inside another wake_up(), but they
> will never refer to the same lock instance.
> Think about:
>
> dfd = socket(...);
> efd1 = epoll_create();
> efd2 = epoll_create();
> epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
>
> When a packet arrives to the device underneath "dfd", the net code will
> issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
> callback wakeup entry on that queue, and the wake_up() performed by the
> "dfd" net code will end up in ep_poll_callback(). At this point epoll
> (efd1) notices that it may have some event ready, so it needs to wake up
> the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
> that ends up in another wake_up(), after having checked about the
> recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
> avoid stack blasting. Never hit the same queue, to avoid loops like:
>
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
> epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...);
> epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...);
> epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...);
>
> The code "if (tncur->wq == wq || ..." prevents re-entering the same
> queue/lock.
Since the epoll code is very careful to not nest same instance locks
allow the recursion.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-04 22:27:20 -08:00
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2009-03-31 15:24:20 -07:00
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lockdep: annotate epoll
On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote:
> I remember I talked with Arjan about this time ago. Basically, since 1)
> you can drop an epoll fd inside another epoll fd 2) callback-based wakeups
> are used, you can see a wake_up() from inside another wake_up(), but they
> will never refer to the same lock instance.
> Think about:
>
> dfd = socket(...);
> efd1 = epoll_create();
> efd2 = epoll_create();
> epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
>
> When a packet arrives to the device underneath "dfd", the net code will
> issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
> callback wakeup entry on that queue, and the wake_up() performed by the
> "dfd" net code will end up in ep_poll_callback(). At this point epoll
> (efd1) notices that it may have some event ready, so it needs to wake up
> the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
> that ends up in another wake_up(), after having checked about the
> recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
> avoid stack blasting. Never hit the same queue, to avoid loops like:
>
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
> epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...);
> epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...);
> epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...);
>
> The code "if (tncur->wq == wq || ..." prevents re-entering the same
> queue/lock.
Since the epoll code is very careful to not nest same instance locks
allow the recursion.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-04 22:27:20 -08:00
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2017-07-03 20:14:56 -04:00
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2017-03-05 12:07:33 +01:00
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2017-07-03 20:14:56 -04:00
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2023-03-07 23:31:58 -08:00
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2017-03-05 12:07:33 +01:00
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2017-07-03 20:14:56 -04:00
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2017-03-05 12:07:33 +01:00
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2017-07-03 20:14:56 -04:00
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2017-03-05 12:07:33 +01:00
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2019-10-16 15:13:41 +01:00
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2019-09-24 16:07:45 +01:00
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lockdep: annotate epoll
On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote:
> I remember I talked with Arjan about this time ago. Basically, since 1)
> you can drop an epoll fd inside another epoll fd 2) callback-based wakeups
> are used, you can see a wake_up() from inside another wake_up(), but they
> will never refer to the same lock instance.
> Think about:
>
> dfd = socket(...);
> efd1 = epoll_create();
> efd2 = epoll_create();
> epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
>
> When a packet arrives to the device underneath "dfd", the net code will
> issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
> callback wakeup entry on that queue, and the wake_up() performed by the
> "dfd" net code will end up in ep_poll_callback(). At this point epoll
> (efd1) notices that it may have some event ready, so it needs to wake up
> the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
> that ends up in another wake_up(), after having checked about the
> recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
> avoid stack blasting. Never hit the same queue, to avoid loops like:
>
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
> epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...);
> epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...);
> epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...);
>
> The code "if (tncur->wq == wq || ..." prevents re-entering the same
> queue/lock.
Since the epoll code is very careful to not nest same instance locks
allow the recursion.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-04 22:27:20 -08:00
|
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|
wait: add wake_up_pollfree()
Several ->poll() implementations are special in that they use a
waitqueue whose lifetime is the current task, rather than the struct
file as is normally the case. This is okay for blocking polls, since a
blocking poll occurs within one task; however, non-blocking polls
require another solution. This solution is for the queue to be cleared
before it is freed, using 'wake_up_poll(wq, EPOLLHUP | POLLFREE);'.
However, that has a bug: wake_up_poll() calls __wake_up() with
nr_exclusive=1. Therefore, if there are multiple "exclusive" waiters,
and the wakeup function for the first one returns a positive value, only
that one will be called. That's *not* what's needed for POLLFREE;
POLLFREE is special in that it really needs to wake up everyone.
Considering the three non-blocking poll systems:
- io_uring poll doesn't handle POLLFREE at all, so it is broken anyway.
- aio poll is unaffected, since it doesn't support exclusive waits.
However, that's fragile, as someone could add this feature later.
- epoll doesn't appear to be broken by this, since its wakeup function
returns 0 when it sees POLLFREE. But this is fragile.
Although there is a workaround (see epoll), it's better to define a
function which always sends POLLFREE to all waiters. Add such a
function. Also make it verify that the queue really becomes empty after
all waiters have been woken up.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211209010455.42744-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2021-12-08 17:04:51 -08:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:19 +02:00
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2017-03-05 12:07:33 +01:00
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2022-09-27 21:02:34 +02:00
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2013-10-02 11:22:21 +02:00
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2017-03-05 10:33:16 +01:00
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2016-09-06 16:00:55 +02:00
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2014-04-18 15:07:17 -07:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2013-10-02 11:22:21 +02:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2015-02-03 12:55:31 +01:00
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2017-03-05 12:07:33 +01:00
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2015-02-03 12:55:31 +01:00
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2017-03-05 12:07:33 +01:00
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freezer,sched: Rewrite core freezer logic
Rewrite the core freezer to behave better wrt thawing and be simpler
in general.
By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is
ensured frozen tasks stay frozen until thawed and don't randomly wake
up early, as is currently possible.
As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up
two PF_flags (yay!).
Specifically; the current scheme works a little like:
freezer_do_not_count();
schedule();
freezer_count();
And either the task is blocked, or it lands in try_to_freezer()
through freezer_count(). Now, when it is blocked, the freezer
considers it frozen and continues.
However, on thawing, once pm_freezing is cleared, freezer_count()
stops working, and any random/spurious wakeup will let a task run
before its time.
That is, thawing tries to thaw things in explicit order; kernel
threads and workqueues before doing bringing SMP back before userspace
etc.. However due to the above mentioned races it is entirely possible
for userspace tasks to thaw (by accident) before SMP is back.
This can be a fatal problem in asymmetric ISA architectures (eg ARMv9)
where the userspace task requires a special CPU to run.
As said; replace this with a special task state TASK_FROZEN and add
the following state transitions:
TASK_FREEZABLE -> TASK_FROZEN
__TASK_STOPPED -> TASK_FROZEN
__TASK_TRACED -> TASK_FROZEN
The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL
(IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state
is already required to deal with spurious wakeups and the freezer
causes one such when thawing the task (since the original state is
lost).
The special __TASK_{STOPPED,TRACED} states *can* be restored since
their canonical state is in ->jobctl.
With this, frozen tasks need an explicit TASK_FROZEN wakeup and are
free of undue (early / spurious) wakeups.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
2022-08-22 13:18:22 +02:00
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2014-10-29 12:21:57 +01:00
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2016-02-23 22:39:28 +09:00
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2017-03-05 12:07:33 +01:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2014-08-24 17:12:27 +00:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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freezer,sched: Rewrite core freezer logic
Rewrite the core freezer to behave better wrt thawing and be simpler
in general.
By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is
ensured frozen tasks stay frozen until thawed and don't randomly wake
up early, as is currently possible.
As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up
two PF_flags (yay!).
Specifically; the current scheme works a little like:
freezer_do_not_count();
schedule();
freezer_count();
And either the task is blocked, or it lands in try_to_freezer()
through freezer_count(). Now, when it is blocked, the freezer
considers it frozen and continues.
However, on thawing, once pm_freezing is cleared, freezer_count()
stops working, and any random/spurious wakeup will let a task run
before its time.
That is, thawing tries to thaw things in explicit order; kernel
threads and workqueues before doing bringing SMP back before userspace
etc.. However due to the above mentioned races it is entirely possible
for userspace tasks to thaw (by accident) before SMP is back.
This can be a fatal problem in asymmetric ISA architectures (eg ARMv9)
where the userspace task requires a special CPU to run.
As said; replace this with a special task state TASK_FROZEN and add
the following state transitions:
TASK_FREEZABLE -> TASK_FROZEN
__TASK_STOPPED -> TASK_FROZEN
__TASK_TRACED -> TASK_FROZEN
The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL
(IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state
is already required to deal with spurious wakeups and the freezer
causes one such when thawing the task (since the original state is
lost).
The special __TASK_{STOPPED,TRACED} states *can* be restored since
their canonical state is in ->jobctl.
With this, frozen tasks need an explicit TASK_FROZEN wakeup and are
free of undue (early / spurious) wakeups.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
2022-08-22 13:18:22 +02:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2015-05-08 18:19:05 +10:00
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2017-03-05 12:07:33 +01:00
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2015-05-08 18:19:05 +10:00
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2017-03-05 12:07:33 +01:00
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2013-11-14 15:16:16 +11:00
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2017-03-05 12:07:33 +01:00
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2013-11-14 15:16:16 +11:00
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2014-01-22 01:22:06 +09:00
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2013-11-14 15:16:16 +11:00
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2017-03-05 12:07:33 +01:00
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2013-11-14 15:16:16 +11:00
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2017-03-05 12:07:33 +01:00
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2013-11-14 15:16:16 +11:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:24 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2013-05-24 15:55:09 -07:00
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2014-08-24 17:12:27 +00:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2019-07-26 20:30:50 +02:00
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2022-06-27 11:50:51 +02:00
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2017-03-05 12:07:33 +01:00
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2013-05-07 16:18:43 -07:00
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2017-03-05 12:07:33 +01:00
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2013-05-07 16:18:43 -07:00
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2017-03-05 12:07:33 +01:00
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2013-05-07 16:18:43 -07:00
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2017-03-05 12:07:33 +01:00
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2013-05-07 16:18:43 -07:00
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2017-07-24 13:58:00 -06:00
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2013-05-07 16:18:43 -07:00
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2017-07-24 13:58:00 -06:00
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2013-05-07 16:18:43 -07:00
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2017-03-05 12:07:33 +01:00
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2013-05-07 16:18:43 -07:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:26 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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2016-07-19 03:04:34 -04:00
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2017-03-05 12:07:33 +01:00
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2016-07-19 03:04:34 -04:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
|
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|
freezer,sched: Rewrite core freezer logic
Rewrite the core freezer to behave better wrt thawing and be simpler
in general.
By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is
ensured frozen tasks stay frozen until thawed and don't randomly wake
up early, as is currently possible.
As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up
two PF_flags (yay!).
Specifically; the current scheme works a little like:
freezer_do_not_count();
schedule();
freezer_count();
And either the task is blocked, or it lands in try_to_freezer()
through freezer_count(). Now, when it is blocked, the freezer
considers it frozen and continues.
However, on thawing, once pm_freezing is cleared, freezer_count()
stops working, and any random/spurious wakeup will let a task run
before its time.
That is, thawing tries to thaw things in explicit order; kernel
threads and workqueues before doing bringing SMP back before userspace
etc.. However due to the above mentioned races it is entirely possible
for userspace tasks to thaw (by accident) before SMP is back.
This can be a fatal problem in asymmetric ISA architectures (eg ARMv9)
where the userspace task requires a special CPU to run.
As said; replace this with a special task state TASK_FROZEN and add
the following state transitions:
TASK_FREEZABLE -> TASK_FROZEN
__TASK_STOPPED -> TASK_FROZEN
__TASK_TRACED -> TASK_FROZEN
The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL
(IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state
is already required to deal with spurious wakeups and the freezer
causes one such when thawing the task (since the original state is
lost).
The special __TASK_{STOPPED,TRACED} states *can* be restored since
their canonical state is in ->jobctl.
With this, frozen tasks need an explicit TASK_FROZEN wakeup and are
free of undue (early / spurious) wakeups.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
2022-08-22 13:18:22 +02:00
|
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2014-10-29 12:21:57 +01:00
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2018-02-13 08:22:36 +11:00
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2017-06-20 12:06:13 +02:00
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2014-10-29 12:21:57 +01:00
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2017-03-05 12:07:33 +01:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
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2017-03-07 15:33:14 -08:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
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2017-03-07 15:33:14 -08:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
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2017-03-07 15:33:14 -08:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
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2017-03-07 15:33:14 -08:00
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2010-05-05 12:53:11 +02:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2007-12-06 12:00:00 -05:00
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2017-07-24 13:58:00 -06:00
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2007-12-06 12:00:00 -05:00
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2017-07-24 13:58:00 -06:00
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2007-12-06 12:00:00 -05:00
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2017-03-05 12:07:33 +01:00
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2007-12-06 12:00:00 -05:00
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2022-08-22 13:18:21 +02:00
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2017-08-18 15:15:55 -07:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:33 +02:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:28 +02:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2017-03-05 12:07:33 +01:00
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2012-11-30 11:42:40 +01:00
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2018-10-10 03:23:09 +00:00
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2017-03-05 12:07:33 +01:00
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2018-10-10 03:23:09 +00:00
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2017-03-05 12:07:33 +01:00
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2013-10-02 11:22:29 +02:00
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2013-08-22 17:45:36 +02:00
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2013-10-04 10:24:49 +02:00
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2017-03-05 12:07:33 +01:00
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2013-08-22 17:45:36 +02:00
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2017-03-05 12:07:33 +01:00
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2013-08-22 17:45:36 +02:00
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2017-03-05 12:07:33 +01:00
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2018-10-10 03:23:09 +00:00
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2017-03-05 12:07:33 +01:00
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2013-08-22 17:45:36 +02:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 11:10:18 +01:00
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2021-06-07 13:26:13 +02:00
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2017-03-05 11:10:18 +01:00
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2017-03-05 10:33:16 +01:00
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2005-04-16 15:20:36 -07:00
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2017-03-05 12:07:33 +01:00
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|
sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2005-04-16 15:20:36 -07:00
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2009-04-28 02:24:21 -07:00
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2017-03-05 12:07:33 +01:00
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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.
Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.
To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:
struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry
For example, this code:
rqw->wait.task_list.next != &wait->task_list
... is was pretty unclear (to me) what it's doing, while now it's written this way:
rqw->wait.head.next != &wait->entry
... which makes it pretty clear that we are iterating a list until we see the head.
Other examples are:
list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {
... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:
list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 12:06:46 +02:00
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2017-03-05 12:07:33 +01:00
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2005-04-16 15:20:36 -07:00
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2021-09-21 21:54:32 +02:00
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sched/core: Add function to sample state of locked-down task
A running task's state can be sampled in a consistent manner (for example,
for diagnostic purposes) simply by invoking smp_call_function_single()
on its CPU, which may be obtained using task_cpu(), then having the
IPI handler verify that the desired task is in fact still running.
However, if the task is not running, this sampling can in theory be done
immediately and directly. In practice, the task might start running at
any time, including during the sampling period. Gaining a consistent
sample of a not-running task therefore requires that something be done
to lock down the target task's state.
This commit therefore adds a try_invoke_on_locked_down_task() function
that invokes a specified function if the specified task can be locked
down, returning true if successful and if the specified function returns
true. Otherwise this function simply returns false. Given that the
function passed to try_invoke_on_nonrunning_task() might be invoked with
a runqueue lock held, that function had better be quite lightweight.
The function is passed the target task's task_struct pointer and the
argument passed to try_invoke_on_locked_down_task(), allowing easy access
to task state and to a location for further variables to be passed in
and out.
Note that the specified function will be called even if the specified
task is currently running. The function can use ->on_rq and task_curr()
to quickly and easily determine the task's state, and can return false
if this state is not to the function's liking. The caller of the
try_invoke_on_locked_down_task() would then see the false return value,
and could take appropriate action, for example, trying again later or
sending an IPI if matters are more urgent.
It is expected that use cases such as the RCU CPU stall warning code will
simply return false if the task is currently running. However, there are
use cases involving nohz_full CPUs where the specified function might
instead fall back to an alternative sampling scheme that relies on heavier
synchronization (such as memory barriers) in the target task.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
[ paulmck: Apply feedback from Peter Zijlstra and Steven Rostedt. ]
[ paulmck: Invoke if running to handle feedback from Mathieu Desnoyers. ]
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-03-11 14:23:21 -07:00
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2013-10-04 10:24:49 +02:00
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