Commit c95491ed authored by Mark Rutland's avatar Mark Rutland Committed by Ingo Molnar
Browse files

locking/atomics, workqueue: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()



For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.

However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.

It's possible to transform the bulk of kernel code using the Coccinelle
script below. However, this doesn't handle comments, leaving references
to ACCESS_ONCE() instances which have been removed. As a preparatory
step, this patch converts the workqueue code and comments to use
{READ,WRITE}_ONCE() consistently.

----
virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-12-git-send-email-paulmck@linux.vnet.ibm.com

Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 564cbc87
...@@ -4647,7 +4647,7 @@ static void rebind_workers(struct worker_pool *pool) ...@@ -4647,7 +4647,7 @@ static void rebind_workers(struct worker_pool *pool)
* concurrency management. Note that when or whether * concurrency management. Note that when or whether
* @worker clears REBOUND doesn't affect correctness. * @worker clears REBOUND doesn't affect correctness.
* *
* ACCESS_ONCE() is necessary because @worker->flags may be * WRITE_ONCE() is necessary because @worker->flags may be
* tested without holding any lock in * tested without holding any lock in
* wq_worker_waking_up(). Without it, NOT_RUNNING test may * wq_worker_waking_up(). Without it, NOT_RUNNING test may
* fail incorrectly leading to premature concurrency * fail incorrectly leading to premature concurrency
...@@ -4656,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool) ...@@ -4656,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool)
WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND)); WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
worker_flags |= WORKER_REBOUND; worker_flags |= WORKER_REBOUND;
worker_flags &= ~WORKER_UNBOUND; worker_flags &= ~WORKER_UNBOUND;
ACCESS_ONCE(worker->flags) = worker_flags; WRITE_ONCE(worker->flags, worker_flags);
} }
spin_unlock_irq(&pool->lock); spin_unlock_irq(&pool->lock);
......
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