kernel_optimize_test/ipc
Manfred Spraul c5b2cbdbda ipc/mqueue.c: update/document memory barriers
Update and document memory barriers for mqueue.c:

- ewp->state is read without any locks, thus READ_ONCE is required.

- add smp_aquire__after_ctrl_dep() after the READ_ONCE, we need
  acquire semantics if the value is STATE_READY.

- use wake_q_add_safe()

- document why __set_current_state() may be used:
  Reading task->state cannot happen before the wake_q_add() call,
  which happens while holding info->lock. Thus the spin_unlock()
  is the RELEASE, and the spin_lock() is the ACQUIRE.

For completeness: there is also a 3 CPU scenario, if the to be woken
up task is already on another wake_q.
Then:
- CPU1: spin_unlock() of the task that goes to sleep is the RELEASE
- CPU2: the spin_lock() of the waker is the ACQUIRE
- CPU2: smp_mb__before_atomic inside wake_q_add() is the RELEASE
- CPU3: smp_mb__after_spinlock() inside try_to_wake_up() is the ACQUIRE

Link: http://lkml.kernel.org/r/20191020123305.14715-4-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Waiman Long <longman@redhat.com>
Cc: <1vier1@web.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-02-04 03:05:23 +00:00
..
compat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ipc_sysctl.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mq_sysctl.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
mqueue.c ipc/mqueue.c: update/document memory barriers 2020-02-04 03:05:23 +00:00
msg.c ipc: rename old-style shmctl/semctl/msgctl syscalls 2019-01-25 17:22:50 +01:00
msgutil.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 52 2019-05-24 17:36:42 +02:00
namespace.c ipc: Convert mqueue fs to fs_context 2019-02-28 03:29:29 -05:00
sem.c ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
shm.c ipc: rename old-style shmctl/semctl/msgctl syscalls 2019-01-25 17:22:50 +01:00
syscall.c y2038: remove CONFIG_64BIT_TIME 2019-11-15 14:38:27 +01:00
util.c treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
util.h ipc: fix sparc64 ipc() wrapper 2019-09-07 21:42:25 +02:00