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| author | Michel Lespinasse <walken@google.com> | 2011-03-10 18:48:51 -0800 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2011-03-11 12:23:08 +0100 |
| commit | 37a9d912b24f96a0591773e6e6c3642991ae5a70 (patch) | |
| tree | 5c4d5b9a52e2c533269e589115afbd25b6c8534b /arch/x86 | |
| parent | 522d7decc0370070448a8c28982c8dfd8970489e (diff) | |
| download | linux-3.10-37a9d912b24f96a0591773e6e6c3642991ae5a70.tar.gz linux-3.10-37a9d912b24f96a0591773e6e6c3642991ae5a70.tar.bz2 linux-3.10-37a9d912b24f96a0591773e6e6c3642991ae5a70.zip | |
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 <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com> [tile]
Acked-by: Tony Luck <tony.luck@intel.com> [ia64]
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Simek <monstr@monstr.eu> [microblaze]
Acked-by: David Howells <dhowells@redhat.com> [frv]
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311024851.GC26122@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/futex.h | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h index 1f11ce44e95..884c0b5676f 100644 --- a/arch/x86/include/asm/futex.h +++ b/arch/x86/include/asm/futex.h @@ -109,9 +109,10 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr) return ret; } -static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, - int newval) +static inline int futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr, + int oldval, int newval) { + int ret = 0; #if defined(CONFIG_X86_32) && !defined(CONFIG_X86_BSWAP) /* Real i386 machines have no cmpxchg instruction */ @@ -122,18 +123,19 @@ static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int))) return -EFAULT; - asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %3, %1\n" + asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %4, %2\n" "2:\t.section .fixup, \"ax\"\n" - "3:\tmov %2, %0\n" + "3:\tmov %3, %0\n" "\tjmp 2b\n" "\t.previous\n" _ASM_EXTABLE(1b, 3b) - : "=a" (oldval), "+m" (*uaddr) - : "i" (-EFAULT), "r" (newval), "0" (oldval) + : "+r" (ret), "=a" (oldval), "+m" (*uaddr) + : "i" (-EFAULT), "r" (newval), "1" (oldval) : "memory" ); - return oldval; + *uval = oldval; + return ret; } #endif |