ARM: 7099/1: futex: preserve oldval in SMP __futex_atomic_op
Will Deacon [Fri, 23 Sep 2011 13:34:12 +0000 (14:34 +0100)]
The SMP implementation of __futex_atomic_op clobbers oldval with the
status flag from the exclusive store. This causes it to always read as
zero when performing the FUTEX_OP_CMP_* operation.

This patch updates the ARM __futex_atomic_op implementations to take a
tmp argument, allowing us to store the strex status flag without
overwriting the register containing oldval.

Cc: stable@kernel.org
Reported-by: Minho Ban <mhban@samsung.com>
Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/futex.h

index 8c73900..253cc86 100644 (file)
 
 #ifdef CONFIG_SMP
 
-#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg)     \
+#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg)        \
        smp_mb();                                               \
        __asm__ __volatile__(                                   \
-       "1:     ldrex   %1, [%2]\n"                             \
+       "1:     ldrex   %1, [%3]\n"                             \
        "       " insn "\n"                                     \
-       "2:     strex   %1, %0, [%2]\n"                         \
-       "       teq     %1, #0\n"                               \
+       "2:     strex   %2, %0, [%3]\n"                         \
+       "       teq     %2, #0\n"                               \
        "       bne     1b\n"                                   \
        "       mov     %0, #0\n"                               \
-       __futex_atomic_ex_table("%4")                           \
-       : "=&r" (ret), "=&r" (oldval)                           \
+       __futex_atomic_ex_table("%5")                           \
+       : "=&r" (ret), "=&r" (oldval), "=&r" (tmp)              \
        : "r" (uaddr), "r" (oparg), "Ir" (-EFAULT)              \
        : "cc", "memory")
 
@@ -73,14 +73,14 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 #include <linux/preempt.h>
 #include <asm/domain.h>
 
-#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg)     \
+#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg)        \
        __asm__ __volatile__(                                   \
-       "1:     " T(ldr) "      %1, [%2]\n"                     \
+       "1:     " T(ldr) "      %1, [%3]\n"                     \
        "       " insn "\n"                                     \
-       "2:     " T(str) "      %0, [%2]\n"                     \
+       "2:     " T(str) "      %0, [%3]\n"                     \
        "       mov     %0, #0\n"                               \
-       __futex_atomic_ex_table("%4")                           \
-       : "=&r" (ret), "=&r" (oldval)                           \
+       __futex_atomic_ex_table("%5")                           \
+       : "=&r" (ret), "=&r" (oldval), "=&r" (tmp)              \
        : "r" (uaddr), "r" (oparg), "Ir" (-EFAULT)              \
        : "cc", "memory")
 
@@ -117,7 +117,7 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
        int cmp = (encoded_op >> 24) & 15;
        int oparg = (encoded_op << 8) >> 20;
        int cmparg = (encoded_op << 20) >> 20;
-       int oldval = 0, ret;
+       int oldval = 0, ret, tmp;
 
        if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
                oparg = 1 << oparg;
@@ -129,19 +129,19 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
 
        switch (op) {
        case FUTEX_OP_SET:
-               __futex_atomic_op("mov  %0, %3", ret, oldval, uaddr, oparg);
+               __futex_atomic_op("mov  %0, %4", ret, oldval, tmp, uaddr, oparg);
                break;
        case FUTEX_OP_ADD:
-               __futex_atomic_op("add  %0, %1, %3", ret, oldval, uaddr, oparg);
+               __futex_atomic_op("add  %0, %1, %4", ret, oldval, tmp, uaddr, oparg);
                break;
        case FUTEX_OP_OR:
-               __futex_atomic_op("orr  %0, %1, %3", ret, oldval, uaddr, oparg);
+               __futex_atomic_op("orr  %0, %1, %4", ret, oldval, tmp, uaddr, oparg);
                break;
        case FUTEX_OP_ANDN:
-               __futex_atomic_op("and  %0, %1, %3", ret, oldval, uaddr, ~oparg);
+               __futex_atomic_op("and  %0, %1, %4", ret, oldval, tmp, uaddr, ~oparg);
                break;
        case FUTEX_OP_XOR:
-               __futex_atomic_op("eor  %0, %1, %3", ret, oldval, uaddr, oparg);
+               __futex_atomic_op("eor  %0, %1, %4", ret, oldval, tmp, uaddr, oparg);
                break;
        default:
                ret = -ENOSYS;