4.4-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will.deacon@arm.com
[ Upstream commit 202fb4ef81e3ec765c23bd1e6746a5c25b797d0e ]
If the spinlock "next" ticket wraps around between the initial LDR and the cmpxchg in the LSE version of spin_trylock, then we can erroneously think that we have successfuly acquired the lock because we only check whether the next ticket return by the cmpxchg is equal to the owner ticket in our updated lock word.
This patch fixes the issue by performing a full 32-bit check of the lock word when trying to determine whether or not the CASA instruction updated memory.
Reported-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/spinlock.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -94,8 +94,8 @@ static inline int arch_spin_trylock(arch " cbnz %w1, 1f\n" " add %w1, %w0, %3\n" " casa %w0, %w1, %2\n" - " and %w1, %w1, #0xffff\n" - " eor %w1, %w1, %w0, lsr #16\n" + " sub %w1, %w1, %3\n" + " eor %w1, %w1, %w0\n" "1:") : "=&r" (lockval), "=&r" (tmp), "+Q" (*lock) : "I" (1 << TICKET_SHIFT)