From 202fb4ef81e3ec765c23bd1e6746a5c25b797d0e Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 31 Jan 2018 12:12:20 +0000 Subject: arm64: spinlock: Fix theoretical trylock() A-B-A with LSE atomics 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 Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/spinlock.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index fdb827c7832f..ebdae15d665d 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -87,8 +87,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock) " 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) -- cgit