From 3a5facd09da848193f5bcb0dea098a298bc1a29d Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 8 Jun 2016 15:10:57 +0100 Subject: [PATCH] arm64: spinlock: fix spin_unlock_wait for LSE atomics Commit d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers") fixed spin_unlock_wait for LL/SC-based atomics under the premise that the LSE atomics (in particular, the LDADDA instruction) are indivisible. Unfortunately, these instructions are only indivisible when used with the -AL (full ordering) suffix and, consequently, the same issue can theoretically be observed with LSE atomics, where a later (in program order) load can be speculated before the write portion of the atomic operation. This patch fixes the issue by performing a CAS of the lock once we've established that it's unlocked, in much the same way as the LL/SC code. Fixes: d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers") Signed-off-by: Will Deacon --- arch/arm64/include/asm/spinlock.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index aac64d55cb22..d5c894253e73 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -43,13 +43,17 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) "2: ldaxr %w0, %2\n" " eor %w1, %w0, %w0, ror #16\n" " cbnz %w1, 1b\n" + /* Serialise against any concurrent lockers */ ARM64_LSE_ATOMIC_INSN( /* LL/SC */ " stxr %w1, %w0, %2\n" -" cbnz %w1, 2b\n", /* Serialise against any concurrent lockers */ - /* LSE atomics */ " nop\n" -" nop\n") +" nop\n", + /* LSE atomics */ +" mov %w1, %w0\n" +" cas %w0, %w0, %2\n" +" eor %w1, %w1, %w0\n") +" cbnz %w1, 2b\n" : "=&r" (lockval), "=&r" (tmp), "+Q" (*lock) : : "memory"); -- 2.30.2