From: Will Deacon <will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org Cc: catalin.marinas@arm.com, Will Deacon <will.deacon@arm.com>, <stable@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org> Subject: [PATCH] arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() Date: Mon, 5 Sep 2016 11:56:05 +0100 [thread overview] Message-ID: <1473072965-7272-1-git-send-email-will.deacon@arm.com> (raw) 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(+) 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 */ -- 2.1.4
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From: will.deacon@arm.com (Will Deacon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() Date: Mon, 5 Sep 2016 11:56:05 +0100 [thread overview] Message-ID: <1473072965-7272-1-git-send-email-will.deacon@arm.com> (raw) 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(+) 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 */ -- 2.1.4
next reply other threads:[~2016-09-05 10:56 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-09-05 10:56 Will Deacon [this message] 2016-09-05 10:56 ` [PATCH] arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() Will Deacon 2016-09-09 11:34 ` Catalin Marinas 2016-09-09 11:34 ` Catalin Marinas
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