arm64: spinlock: fix ll/sc unlock on big-endian systems

When unlocking a spinlock, we perform a read-modify-write on the owner
ticket in order to increment it and store it back with release
semantics.

In the LL/SC case, we load the 16-bit ticket using a 32-bit load and
therefore store back the wrong halfword on a big-endian system,
corrupting the lock after the first unlock and killing the system dead.

This patch fixes the unlock code to use 16-bit accessors consistently.

Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index 87ae7ef..c85e96d 100644 (file)
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -110,7 +110,7 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
 
        asm volatile(ARM64_LSE_ATOMIC_INSN(
        /* LL/SC */
-       "       ldr     %w1, %0\n"
+       "       ldrh    %w1, %0\n"
        "       add     %w1, %w1, #1\n"
        "       stlrh   %w1, %0",
        /* LSE atomics */