kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-10-09 18:15:49 +00:00
Code Issues Releases Packages Activity
No description
890,253 commits 116 branches 5,788 tags 5.6 GiB
  • C 96.9%
  • Assembly 0.9%
  • Rust 0.6%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Neeraj Upadhyay 4f50dbf293 rcu: Allow only one expedited GP to run concurrently with wakeups 
commit 4bc6b745e5 upstream.

The current expedited RCU grace-period code expects that a task
requesting an expedited grace period cannot awaken until that grace
period has reached the wakeup phase.  However, it is possible for a long
preemption to result in the waiting task never sleeping.  For example,
consider the following sequence of events:

1.	Task A starts an expedited grace period by invoking
	synchronize_rcu_expedited().  It proceeds normally up to the
	wait_event() near the end of that function, and is then preempted
	(or interrupted or whatever).

2.	The expedited grace period completes, and a kworker task starts
	the awaken phase, having incremented the counter and acquired
	the rcu_state structure's .exp_wake_mutex.  This kworker task
	is then preempted or interrupted or whatever.

3.	Task A resumes and enters wait_event(), which notes that the
	expedited grace period has completed, and thus doesn't sleep.

4.	Task B starts an expedited grace period exactly as did Task A,
	complete with the preemption (or whatever delay) just before
	the call to wait_event().

5.	The expedited grace period completes, and another kworker
	task starts the awaken phase, having incremented the counter.
	However, it blocks when attempting to acquire the rcu_state
	structure's .exp_wake_mutex because step 2's kworker task has
	not yet released it.

6.	Steps 4 and 5 repeat, resulting in overflow of the rcu_node
	structure's ->exp_wq[] array.

In theory, this is harmless.  Tasks waiting on the various ->exp_wq[]
array will just be spuriously awakened, but they will just sleep again
on noting that the rcu_state structure's ->expedited_sequence value has
not advanced far enough.

In practice, this wastes CPU time and is an accident waiting to happen.
This commit therefore moves the rcu_exp_gp_seq_end() call that officially
ends the expedited grace period (along with associate tracing) until
after the ->exp_wake_mutex has been acquired.  This prevents Task A from
awakening prematurely, thus preventing more than one expedited grace
period from being in flight during a previous expedited grace period's
wakeup phase.

Fixes: 3b5f668e71 ("rcu: Overlap wakeups with next expedited grace period")
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
[ paulmck: Added updated comment. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2020-03-05 16:45:24 +01:00
arch KVM: x86: Remove spurious clearing of async #PF MSR 2020-03-05 16:45:24 +01:00
block block, bfq: do not plug I/O for bfq_queues with no proc refs 2020-02-24 08:38:09 +01:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto crypto: rename sm3-256 to sm3 in hash_algo_name 2020-02-28 17:23:43 +01:00
Documentation docs: Fix empty parallelism argument 2020-03-05 16:45:14 +01:00
drivers pwm: omap-dmtimer: put_device() after of_find_device_by_node() 2020-03-05 16:45:23 +01:00
fs f2fs: fix to add swap extent correctly 2020-03-05 16:45:22 +01:00
include lib/vdso: Make __arch_update_vdso_data() logic understandable 2020-03-05 16:45:22 +01:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-28 17:23:36 +01:00
kernel rcu: Allow only one expedited GP to run concurrently with wakeups 2020-03-05 16:45:24 +01:00
lib crypto: chacha20poly1305 - prevent integer overflow on large input 2020-02-28 17:23:40 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: Avoid creating virtual address aliases in brk()/mmap()/mremap() 2020-02-28 17:23:37 +01:00
net tipc: fix successful connect() but timed out 2020-03-05 16:45:21 +01:00
samples samples/bpf: Set -fno-stack-protector when building BPF programs 2020-02-24 08:38:15 +01:00
scripts kbuild: fix DT binding schema rule to detect command line changes 2020-03-05 16:45:19 +01:00
security ima: ima/lsm policy rule loading logic bug fixes 2020-03-05 16:45:22 +01:00
sound ASoC: SOF: Intel: hda: Add iDisp4 DAI 2020-02-28 17:23:45 +01:00
tools perf maps: Add missing unlock to maps__insert() error case 2020-03-05 16:45:23 +01:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt KVM: Check for a bad hva before dropping into the ghc slow path 2020-03-05 16:45:21 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap MAINTAINERS: update my email address 2020-01-11 14:33:39 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:23:36 +01:00
Makefile Linux 5.5.7 2020-02-28 17:23:45 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.