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ARM: 7955/1: spinlock: ensure we have a compiler barrier before sev

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When unlocking a spinlock, we require the following, strictly ordered
sequence of events:

	<barrier>	/* dmb */
	<unlock>
	<barrier>	/* dsb */
	<sev>

Whilst the code does indeed reflect this in terms of the architecture,
the final <barrier> + <sev> have been contracted into a single inline
asm without a "memory" clobber, therefore the compiler is at liberty to
reorder the unlock to the end of the above sequence. In such a case,
a waiting CPU may be woken up before the lock has been unlocked, leading
to extremely poor performance.

This patch reworks the dsb_sev() function to make use of the dsb()
macro and ensure ordering against the unlock.

Cc: <stable@vger.kernel.org>
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Will Deacon 2014-02-07 19:12:32 +01:00 committed by Russell King
parent bae0ca2bc5
commit 7c8746a9eb
1 changed files with 3 additions and 12 deletions
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15
arch/arm/include/asm/spinlock.h
View file

@ -37,18 +37,9 @@
static inline void dsb_sev(void)
{
#if __LINUX_ARM_ARCH__ >= 7
__asm__ __volatile__ (
"dsb ishst\n"
SEV
);
#else
__asm__ __volatile__ (
"mcr p15, 0, %0, c7, c10, 4\n"
SEV
: : "r" (0)
);
#endif
dsb(ishst);
__asm__(SEV);
}
/*