This is a note to let you know that I've just added the patch titled
metag: fix memory barriers
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
metag-fix-memory-barriers.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2425ce84026c385b73ae72039f90d042d49e0394 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Thu, 8 May 2014 15:51:37 -0400
Subject: metag: fix memory barriers
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
commit 2425ce84026c385b73ae72039f90d042d49e0394 upstream.
Volatile access doesn't really imply the compiler barrier. Volatile access
is only ordered with respect to other volatile accesses, it isn't ordered
with respect to general memory accesses. Gcc may reorder memory accesses
around volatile access, as we can see in this simple example (if we
compile it with optimization, both increments of *b will be collapsed to
just one):
void fn(volatile int *a, long *b)
{
(*b)++;
*a = 10;
(*b)++;
}
Consequently, we need the compiler barrier after a write to the volatile
variable, to make sure that the compiler doesn't reorder the volatile
write with something else.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/metag/include/asm/barrier.h | 3 +++
1 file changed, 3 insertions(+)
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -15,6 +15,7 @@ static inline void wr_fence(void)
volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_FENCE;
barrier();
*flushptr = 0;
+ barrier();
}
#else /* CONFIG_METAG_META21 */
@@ -35,6 +36,7 @@ static inline void wr_fence(void)
*flushptr = 0;
*flushptr = 0;
*flushptr = 0;
+ barrier();
}
#endif /* !CONFIG_METAG_META21 */
@@ -68,6 +70,7 @@ static inline void fence(void)
volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK;
barrier();
*flushptr = 0;
+ barrier();
}
#define smp_mb() fence()
#define smp_rmb() fence()
Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are
queue-3.10/metag-fix-memory-barriers.patch
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