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| author | Peter Zijlstra <peterz@infradead.org> | 2016-09-05 11:37:53 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-08-10 12:29:02 +0200 |
| commit | d89e588ca4081615216cc25f2489b0281ac0bfe9 (patch) | |
| tree | 9f3fd5958adb8b6a0a86065ca0c0603fc73c3c06 /include/linux/atomic.h | |
| parent | ff7a5fb0f1d510997a845e0d227f30831ff38d9d (diff) | |
| download | linux-0-day-d89e588ca4081615216cc25f2489b0281ac0bfe9.tar.gz linux-0-day-d89e588ca4081615216cc25f2489b0281ac0bfe9.tar.xz | |
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 'include/linux/atomic.h')
| -rw-r--r-- | include/linux/atomic.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/atomic.h b/include/linux/atomic.h index c56be74101305..40d6bfec0e0d0 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -38,6 +38,9 @@ * Besides, if an arch has a special barrier for acquire/release, it could * implement its own __atomic_op_* and use the same framework for building * variants + * + * If an architecture overrides __atomic_op_acquire() it will probably want + * to define smp_mb__after_spinlock(). */ #ifndef __atomic_op_acquire #define __atomic_op_acquire(op, args...) \ |