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Jakub Kicinski 747056a9a9 Merge branch 'net-ipa-simplify-tx-power-handling' 
Alex Elder says:

====================
net: ipa: simplify TX power handling

In order to deliver a packet to the IPA hardware, we must ensure
it is powered.  We request power by calling pm_runtime_get(), and
its return value tells us the power state.  We can't block in
ipa_start_xmit(), so if power isn't enabled we prevent further
transmit attempts by calling netif_stop_queue().  Power will
eventually become enabled, at which point we call netif_wake_queue()
to allow the transmit to be retried.  When it does, the power should
be enabled, so the packet delivery can proceed.

The logic that handles this is convoluted, and was put in place
to address a race condition pointed out by Jakub Kicinski during
review.  The fix addressed that race, as well as another one that
was found while investigating it:
  b8e36e13ea ("net: ipa: fix TX queue race")
I have wanted to simplify this code ever since, and I'm pleased to
report that this series implements a much better solution that
avoids both race conditions.

The first race occurs between the ->ndo_start_xmit thread and the
runtime resume thread.  If we find power is not enabled when
requested in ipa_start_xmit(), we stop queueing.  But there's a
chance the runtime resume will enable queuing just before that,
leaving queueing stopped forever.  A flag is used to ensure that
does not occur.

A second flag is used to prevent NETDEV_TX_BUSY from being returned
repeatedly during the small window between enabling queueing and
finishing power resume.  This can happen if resume was underway when
pm_runtime_get() was called and completes immediately afterward.
This condition only exists because of the use of the first flag.

The fix is to disable transmit for *every* call to ipa_start_xmit(),
disabling it *before* calling pm_runtime_get().  This leaves three
cases:
  - If the return value indicates power is not active (or is in
    transition), queueing remains disabled--thereby avoiding
    the race between disabling it and a concurrent power thread
    enabling it.
  - If pm_runtime_get() returns an error, we drop the packet and
    re-enable queueing.
  - Finally, if the hardware is powered, we re-enable queueing
    before delivering the packet to the hardware.

So the first race is avoided.  And as a result, the second condition
will not occur.

The first patch adds pointers to the TX and RX IPA endpoints in the
netdev private data.  The second patch has netif_stop_queue() be
called for all packets; if pm_runtime_get() indicates power is
enabled (or an error), netif_wake_queue() is called to enable it
again.  The third and fourth patches get rid of the STARTED and
STOPPED IPA power flags, as well as the power spinlock, because they
are no longer needed.  The last three patches just eliminate some
trivial functions, open-coding them instead.
====================

Link: https://lore.kernel.org/r/20240130192305.250915-1-elder@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
History 2024-02-01 20:55:09 -08:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
block block: Fix WARNING in _copy_from_iter 2024-01-23 08:56:55 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto crypto: scomp - fix req->dst buffer overflow 2023-12-29 11:25:56 +08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
drivers net: ipa: kill ipa_power_modem_queue_wake() 2024-02-01 20:50:36 -08:00
fs Description for this pull request: 2024-02-01 11:45:53 -08:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
init init: Kconfig: Disable -Wstringop-overflow for GCC-11 2024-01-21 17:45:31 -06:00
io_uring io_uring: enable audit and restrict cred override for IORING_OP_FIXED_FD_INSTALL 2024-01-23 15:25:14 -07:00
ipc shm: Slim down dependencies 2023-12-20 19:26:31 -05:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm 22 hotfixes. 11 are cc:stable and the remainder address post-6.7 issues 2024-01-29 17:12:16 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
rust rust: phy: use VTABLE_DEFAULT_ERROR 2024-01-27 14:28:00 +00:00
samples samples/cgroup: add .gitignore file for generated samples 2024-01-24 11:52:40 -08:00
scripts Kbuild fixes for v6.8 2024-02-01 11:57:42 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
sound sound fixes for 6.8-rc1 2024-01-19 12:30:29 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt Generic: 2024-01-17 13:03:37 -08:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.mailmap mailmap: add entry for Stefan Wahren 2024-01-31 13:38:51 +00:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: supplement of zswap maintainers update 2024-01-25 23:52:21 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-02-01 15:12:37 -08:00
Makefile Kbuild fixes for v6.8 2024-02-01 11:57:42 -08:00
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.