2019-05-27 14:55:01 +08:00
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/* SPDX-License-Identifier: GPL-2.0-or-later */
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2005-04-17 06:20:36 +08:00
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#ifndef __ASM_SPINLOCK_H
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#define __ASM_SPINLOCK_H
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2005-12-17 05:43:46 +08:00
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#ifdef __KERNEL__
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2005-04-17 06:20:36 +08:00
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2020-07-24 21:14:19 +08:00
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#include <asm/simple_spinlock.h>
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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>
2016-09-05 17:37:53 +08:00
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2005-12-17 05:43:46 +08:00
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#endif /* __KERNEL__ */
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2005-04-17 06:20:36 +08:00
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#endif /* __ASM_SPINLOCK_H */
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