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>
diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index 7c589ef..631e8da 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -82,35 +82,37 @@
}
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;
+ int ret = 0, prev;
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
return -EFAULT;
__asm__ __volatile__ (
PPC_RELEASE_BARRIER
-"1: lwarx %0,0,%2 # futex_atomic_cmpxchg_inatomic\n\
- cmpw 0,%0,%3\n\
+"1: lwarx %1,0,%3 # futex_atomic_cmpxchg_inatomic\n\
+ cmpw 0,%1,%4\n\
bne- 3f\n"
- PPC405_ERR77(0,%2)
-"2: stwcx. %4,0,%2\n\
+ PPC405_ERR77(0,%3)
+"2: stwcx. %5,0,%3\n\
bne- 1b\n"
PPC_ACQUIRE_BARRIER
"3: .section .fixup,\"ax\"\n\
-4: li %0,%5\n\
+4: li %0,%6\n\
b 3b\n\
.previous\n\
.section __ex_table,\"a\"\n\
.align 3\n\
" PPC_LONG "1b,4b,2b,4b\n\
.previous" \
- : "=&r" (prev), "+m" (*uaddr)
+ : "+r" (ret), "=&r" (prev), "+m" (*uaddr)
: "r" (uaddr), "r" (oldval), "r" (newval), "i" (-EFAULT)
: "cc", "memory");
- return prev;
+ *uval = prev;
+ return ret;
}
#endif /* __KERNEL__ */