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locking: Remove ACCESS_ONCE() usage

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With the new standardized functions, we can replace all
ACCESS_ONCE() calls across relevant locking - this includes
lockref and seqlock while at it.

ACCESS_ONCE() does not work reliably on non-scalar types.
For example gcc 4.6 and 4.7 might remove the volatile tag
for such accesses during the SRA (scalar replacement of
aggregates) step:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145

Update the new calls regardless of if it is a scalar type,
this is cleaner than having three alternatives.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1424662301.6539.18.camel@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Davidlohr Bueso
2015-02-22 19:31:41 -08:00
committed by Ingo Molnar
parent 2ae7902681
commit 4d3199e4ca
6 changed files with 23 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
kernel/locking/mcs_spinlock.h
View File

@@ -78,7 +78,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
*/
return;
}
ACCESS_ONCE(prev->next) = node;
WRITE_ONCE(prev->next, node);
/* Wait until the lock holder passes the lock down. */
arch_mcs_spin_lock_contended(&node->locked);
@@ -91,7 +91,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
static inline
void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
{
struct mcs_spinlock *next = ACCESS_ONCE(node->next);
struct mcs_spinlock *next = READ_ONCE(node->next);
if (likely(!next)) {
/*
@@ -100,7 +100,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
if (likely(cmpxchg(lock, node, NULL) == node))
return;
/* Wait until the next pointer is set */
while (!(next = ACCESS_ONCE(node->next)))
while (!(next = READ_ONCE(node->next)))
cpu_relax_lowlatency();
}