Commit 872c63fb authored Sep 05, 2016 by Will Deacon Committed by Catalin Marinas Sep 09, 2016

arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb()



smp_mb__before_spinlock() is intended to upgrade a spin_lock() operation
to a full barrier, such that prior stores are ordered with respect to
loads and stores occuring inside the critical section.

Unfortunately, the core code defines the barrier as smp_wmb(), which
is insufficient to provide the required ordering guarantees when used in
conjunction with our load-acquire-based spinlock implementation.

This patch overrides the arm64 definition of smp_mb__before_spinlock()
to map to a full smp_mb().

Cc: <stable@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent c6935931

arch/arm64/include/asm/spinlock.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -363,4 +363,14 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
		#define arch_read_relax(lock) cpu_relax()
		#define arch_write_relax(lock) cpu_relax()

		/*
		* Accesses appearing in program order before a spin_lock() operation
		* can be reordered with accesses inside the critical section, by virtue
		* of arch_spin_lock being constructed using acquire semantics.
		*
		* In cases where this is problematic (e.g. try_to_wake_up), an
		* smp_mb__before_spinlock() can restore the required ordering.
		*/
		#define smp_mb__before_spinlock() smp_mb()

		#endif /* __ASM_SPINLOCK_H */