arm64: spinlock: Fix theoretical trylock() A-B-A with LSE atomics
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Web: https://git.kernel.org/torvalds/c/202fb4ef81e3ec765c23bd1e6746a5c25b797d0e Commit: 202fb4ef81e3ec765c23bd1e6746a5c25b797d0e Parent: ec89ab50a03a33a4a648869e868b1964354fb2d1 Refname: refs/heads/master Author: Will Deacon <[email protected]> AuthorDate: Wed Jan 31 12:12:20 2018 +0000 Committer: Catalin Marinas <[email protected]> CommitDate: Tue Feb 6 22:53:11 2018 +0000 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 <[email protected]> Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Catalin Marinas <[email protected]> --- 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) -- To unsubscribe from this list: send the line "unsubscribe git-commits-head" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html