Commit-ID: c95491ed6d6a958743d82bea1d053819988da418
Gitweb: https://git.kernel.org/tip/c95491ed6d6a958743d82bea1d053819988da418
Author: Mark Rutland <mark.rutl...@arm.com>
AuthorDate: Mon, 23 Oct 2017 14:07:22 -0700
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Wed, 25 Oct 2017 11:01:03 +0200
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: Mark Rutland <mark.rutl...@arm.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Acked-by: Tejun Heo <t...@kernel.org>
Cc: Lai Jiangshan <jiangshan...@gmail.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: da...@davemloft.net
Cc: linux-a...@vger.kernel.org
Cc: m...@ellerman.id.au
Cc: sh...@kernel.org
Cc: snit...@redhat.com
Cc: thor.tha...@linux.intel.com
Cc: v...@zeniv.linux.org.uk
Cc: will.dea...@arm.com
Link:
http://lkml.kernel.org/r/1508792849-3115-12-git-send-email-paul...@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/workqueue.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 64d0edf..39831b2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4647,7 +4647,7 @@ static void rebind_workers(struct worker_pool *pool)
* concurrency management. Note that when or whether
* @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
* wq_worker_waking_up(). Without it, NOT_RUNNING test may
* fail incorrectly leading to premature concurrency
@@ -4656,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool)
WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
worker_flags |= WORKER_REBOUND;
worker_flags &= ~WORKER_UNBOUND;
- ACCESS_ONCE(worker->flags) = worker_flags;
+ WRITE_ONCE(worker->flags, worker_flags);
}
spin_unlock_irq(&pool->lock);
