[12/19] workqueue: Kill off ACCESS_ONCE()

Message ID 1508792849-3115-12-git-send-email-paulmck@linux.vnet.ibm.com
State New
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Series
  • [01/19] dm integrity: Kill off ACCESS_ONCE()
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Commit Message

Paul E. McKenney Oct. 23, 2017, 9:07 p.m.
From: Mark Rutland <mark.rutland@arm.com>


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.rutland@arm.com>

Acked-by: Tejun Heo <tj@kernel.org>

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
---
 kernel/workqueue.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
2.5.2

Patch

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 64d0edf428f8..39831b2f3c5f 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);