| Message ID | 1473072965-7272-1-git-send-email-will.deacon@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Sep 05, 2016 at 11:56:05AM +0100, Will Deacon wrote: > 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> Queued for -rc6. Thanks.
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index e875a5a551d7..89206b568cd4 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -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 */
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> --- arch/arm64/include/asm/spinlock.h | 10 ++++++++++ 1 file changed, 10 insertions(+)