Commit ca88b6d9 authored by Will Deacon's avatar Will Deacon Committed by Ben Hutchings

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

commit 872c63fb upstream.

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: Peter Zijlstra <peterz@infradead.org>
Reported-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 21274362
......@@ -231,4 +231,14 @@ 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 */
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