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authorPeter Zijlstra <peterz@infradead.org>2016-09-05 11:37:53 +0200
committerIngo Molnar <mingo@kernel.org>2017-08-10 12:29:02 +0200
commitd89e588ca4081615216cc25f2489b0281ac0bfe9 (patch)
tree9f3fd5958adb8b6a0a86065ca0c0603fc73c3c06 /arch/arm64/include/asm/spinlock.h
parentoverlayfs, locking: Remove smp_mb__before_spinlock() usage (diff)
downloadlinux-dev-d89e588ca4081615216cc25f2489b0281ac0bfe9.tar.xz
linux-dev-d89e588ca4081615216cc25f2489b0281ac0bfe9.zip
locking: Introduce smp_mb__after_spinlock()
Since its inception, our understanding of ACQUIRE, esp. as applied to spinlocks, has changed somewhat. Also, I wonder if, with a simple change, we cannot make it provide more. The problem with the comment is that the STORE done by spin_lock isn't itself ordered by the ACQUIRE, and therefore a later LOAD can pass over it and cross with any prior STORE, rendering the default WMB insufficient (pointed out by Alan). Now, this is only really a problem on PowerPC and ARM64, both of which already defined smp_mb__before_spinlock() as a smp_mb(). At the same time, we can get a much stronger construct if we place that same barrier _inside_ the spin_lock(). In that case we upgrade the RCpc spinlock to an RCsc. That would make all schedule() calls fully transitive against one another. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to '')
-rw-r--r--arch/arm64/include/asm/spinlock.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index cae331d553f8..b103888b694a 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -367,5 +367,7 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
* smp_mb__before_spinlock() can restore the required ordering.
*/
#define smp_mb__before_spinlock() smp_mb()
+/* See include/linux/spinlock.h */
+#define smp_mb__after_spinlock() smp_mb()
#endif /* __ASM_SPINLOCK_H */