From cf0eda6f5e03b515b826dc7f25da24a91714c71e Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 24 Jun 2012 19:24:42 +0300 Subject: [PATCH] --- yaml --- r: 315854 b: refs/heads/master c: d0a69d6321ca759bb8d47803d06ba8571ab42d07 h: refs/heads/master v: v3 --- [refs] | 2 +- trunk/arch/x86/include/asm/bitops.h | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/[refs] b/[refs] index 06bda073b8d2..7453810f4326 100644 --- a/[refs] +++ b/[refs] @@ -1,2 +1,2 @@ --- -refs/heads/master: ab9cf4996bb989983e73da894b8dd0239aa2c3c2 +refs/heads/master: d0a69d6321ca759bb8d47803d06ba8571ab42d07 diff --git a/trunk/arch/x86/include/asm/bitops.h b/trunk/arch/x86/include/asm/bitops.h index a6983b277220..72f5009deb5a 100644 --- a/trunk/arch/x86/include/asm/bitops.h +++ b/trunk/arch/x86/include/asm/bitops.h @@ -264,6 +264,13 @@ static inline int test_and_clear_bit(int nr, volatile unsigned long *addr) * This operation is non-atomic and can be reordered. * If two examples of this operation race, one can appear to succeed * but actually fail. You must protect multiple accesses with a lock. + * + * Note: the operation is performed atomically with respect to + * the local CPU, but not other CPUs. Portable code should not + * rely on this behaviour. + * KVM relies on this behaviour on x86 for modifying memory that is also + * accessed from a hypervisor on the same CPU if running in a VM: don't change + * this without also updating arch/x86/kernel/kvm.c */ static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr) {