From 37a9d912b24f96a0591773e6e6c3642991ae5a70 Mon Sep 17 00:00:00 2001 From: Michel Lespinasse Date: Thu, 10 Mar 2011 18:48:51 -0800 Subject: futex: Sanitize cmpxchg_futex_value_locked API The cmpxchg_futex_value_locked API was funny in that it returned either the original, user-exposed futex value OR an error code such as -EFAULT. This was confusing at best, and could be a source of livelocks in places that retry the cmpxchg_futex_value_locked after trying to fix the issue by running fault_in_user_writeable(). This change makes the cmpxchg_futex_value_locked API more similar to the get_futex_value_locked one, returning an error code and updating the original value through a reference argument. Signed-off-by: Michel Lespinasse Acked-by: Chris Metcalf [tile] Acked-by: Tony Luck [ia64] Acked-by: Thomas Gleixner Tested-by: Michal Simek [microblaze] Acked-by: David Howells [frv] Cc: Darren Hart Cc: Peter Zijlstra Cc: Matt Turner Cc: Russell King Cc: Ralf Baechle Cc: "James E.J. Bottomley" Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: Paul Mundt Cc: "David S. Miller" Cc: Linus Torvalds LKML-Reference: <20110311024851.GC26122@google.com> Signed-off-by: Thomas Gleixner --- arch/alpha/include/asm/futex.h | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) (limited to 'arch/alpha/include') diff --git a/arch/alpha/include/asm/futex.h b/arch/alpha/include/asm/futex.h index 945de22..c4e5c28 100644 --- a/arch/alpha/include/asm/futex.h +++ b/arch/alpha/include/asm/futex.h @@ -81,21 +81,22 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr) } static inline int -futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval) +futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr, + int oldval, int newval) { - int prev, cmp; + int ret = 0, prev, cmp; if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int))) return -EFAULT; __asm__ __volatile__ ( __ASM_SMP_MB - "1: ldl_l %0,0(%2)\n" - " cmpeq %0,%3,%1\n" - " beq %1,3f\n" - " mov %4,%1\n" - "2: stl_c %1,0(%2)\n" - " beq %1,4f\n" + "1: ldl_l %1,0(%3)\n" + " cmpeq %1,%4,%2\n" + " beq %2,3f\n" + " mov %5,%2\n" + "2: stl_c %2,0(%3)\n" + " beq %2,4f\n" "3: .subsection 2\n" "4: br 1b\n" " .previous\n" @@ -105,11 +106,12 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval) " .long 2b-.\n" " lda $31,3b-2b(%0)\n" " .previous\n" - : "=&r"(prev), "=&r"(cmp) + : "+r"(ret), "=&r"(prev), "=&r"(cmp) : "r"(uaddr), "r"((long)oldval), "r"(newval) : "memory"); - return prev; + *uval = prev; + return ret; } #endif /* __KERNEL__ */ -- cgit v1.1