On Wed, Jul 01, 2015 at 09:39:44AM -0700, Linus Torvalds wrote:
> Peter/Ingo,
> while resolving a conflict, I noticed that we have the generic
> default definition of "smp_store_mb()" be:
>
> do { WRITE_ONCE(var, value); mb(); } while (0)
>
> which looks pretty odd. Why? That "mb()" is a full memory barrier even
> on UP, yet this is clearly a smp barrier.
>
> So I think that "mb()" should be "smp_mb()". Looking at other
> architecture definitions, most architectures already do that.
Agreed.
> I think this is just left-over from our previous (badly specified)
> "set_mb()", and that commit b92b8b35a2e3 ("locking/arch: Rename
> set_mb() to smp_store_mb()") just didn't notice.
That commit was a sed script :-). but yes I should've noticed something
was up when looking at the result.
> Our old set_mb()
> was already confused about whether it was a smp barrier or an IO
> barrier (eg ARM uses smp_mb, x86 has separate smp/up versions, but
> others dop the unconditional memory barrier).
>
> I didn't change this in the merge, because it's not just the generic
> version where the conflict was, there's also powerpc, s390 and ia64
> that still have the non-smp version too. But some locking person
> should probably clean this up... Hint hint,
A quick git grep for smp_store_mb() users throws up all of 7 users, they
all would be fine with smp_mb(). Lemme go do that patch..
git grep -l "smp_store_mb.*\<mb();" | while read file; do sed -i
's/\(smp_store_mb.*\)\<mb();/\1smp_mb();/' $file; done
---
Subject: locking/arch: Make smp_store_mb() use smp_mb()
Linus noticed that there were a few smp_store_mb() implementations that
used mb(), which is inconsistent with the new naming.
Since all smp_store_mb() users really are about SMP ordering, not IO
ordering, change them all to be consistent.
Cc: Tony Luck <tony.l...@intel.com>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Heiko Carstens <heiko.carst...@de.ibm.com>
Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
arch/ia64/include/asm/barrier.h | 2 +-
arch/powerpc/include/asm/barrier.h | 2 +-
arch/s390/include/asm/barrier.h | 2 +-
include/asm-generic/barrier.h | 2 +-
4 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index 843ba435e43b..39ed6515415f 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -77,7 +77,7 @@ do {
\
___p1; \
})
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); }
while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb();
} while (0)
/*
* The group barrier in front of the rsm & ssm are necessary to ensure
diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
index 51ccc7232042..5525268f35c0 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -34,7 +34,7 @@
#define rmb() __asm__ __volatile__ ("sync" : : : "memory")
#define wmb() __asm__ __volatile__ ("sync" : : : "memory")
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); }
while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb();
} while (0)
#ifdef __SUBARCH_HAS_LWSYNC
# define SMPWMB LWSYNC
diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index e6f8615a11eb..a4dea6050c77 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -36,7 +36,7 @@
#define smp_mb__before_atomic() smp_mb()
#define smp_mb__after_atomic() smp_mb()
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value);
mb(); } while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value);
smp_mb(); } while (0)
#define smp_store_release(p, v)
\
do { \
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index e6a83d712ef6..d716aa564931 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -67,7 +67,7 @@
#endif
#ifndef smp_store_mb
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while
(0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
#endif
#ifndef smp_mb__before_atomic
--
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