powerpc: Make {cmp}xchg* and their atomic_ versions fully ordered
authorBoqun Feng <boqun.feng@gmail.com>
Mon, 2 Nov 2015 01:30:32 +0000 (09:30 +0800)
committerBen Hutchings <ben@decadent.org.uk>
Sat, 13 Feb 2016 10:34:05 +0000 (10:34 +0000)
commit 81d7a3294de7e9828310bbf986a67246b13fa01e upstream.

According to memory-barriers.txt, xchg*, cmpxchg* and their atomic_
versions all need to be fully ordered, however they are now just
RELEASE+ACQUIRE, which are not fully ordered.

So also replace PPC_RELEASE_BARRIER and PPC_ACQUIRE_BARRIER with
PPC_ATOMIC_ENTRY_BARRIER and PPC_ATOMIC_EXIT_BARRIER in
__{cmp,}xchg_{u32,u64} respectively to guarantee fully ordered semantics
of atomic{,64}_{cmp,}xchg() and {cmp,}xchg(), as a complement of commit
b97021f85517 ("powerpc: Fix atomic_xxx_return barrier semantics")

This patch depends on patch "powerpc: Make value-returning atomics fully
ordered" for PPC_ATOMIC_ENTRY_BARRIER definition.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[bwh: backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
arch/powerpc/include/asm/system.h

index e30a13d..10d5c3e 100644 (file)
@@ -234,12 +234,12 @@ __xchg_u32(volatile void *p, unsigned long val)
        unsigned long prev;
 
        __asm__ __volatile__(
-       PPC_RELEASE_BARRIER
+       PPC_ATOMIC_ENTRY_BARRIER
 "1:    lwarx   %0,0,%2 \n"
        PPC405_ERR77(0,%2)
 "      stwcx.  %3,0,%2 \n\
        bne-    1b"
-       PPC_ACQUIRE_BARRIER
+       PPC_ATOMIC_EXIT_BARRIER
        : "=&r" (prev), "+m" (*(volatile unsigned int *)p)
        : "r" (p), "r" (val)
        : "cc", "memory");
@@ -277,12 +277,12 @@ __xchg_u64(volatile void *p, unsigned long val)
        unsigned long prev;
 
        __asm__ __volatile__(
-       PPC_RELEASE_BARRIER
+       PPC_ATOMIC_ENTRY_BARRIER
 "1:    ldarx   %0,0,%2 \n"
        PPC405_ERR77(0,%2)
 "      stdcx.  %3,0,%2 \n\
        bne-    1b"
-       PPC_ACQUIRE_BARRIER
+       PPC_ATOMIC_EXIT_BARRIER
        : "=&r" (prev), "+m" (*(volatile unsigned long *)p)
        : "r" (p), "r" (val)
        : "cc", "memory");
@@ -368,14 +368,14 @@ __cmpxchg_u32(volatile unsigned int *p, unsigned long old, unsigned long new)
        unsigned int prev;
 
        __asm__ __volatile__ (
-       PPC_RELEASE_BARRIER
+       PPC_ATOMIC_ENTRY_BARRIER
 "1:    lwarx   %0,0,%2         # __cmpxchg_u32\n\
        cmpw    0,%0,%3\n\
        bne-    2f\n"
        PPC405_ERR77(0,%2)
 "      stwcx.  %4,0,%2\n\
        bne-    1b"
-       PPC_ACQUIRE_BARRIER
+       PPC_ATOMIC_EXIT_BARRIER
        "\n\
 2:"
        : "=&r" (prev), "+m" (*p)
@@ -414,13 +414,13 @@ __cmpxchg_u64(volatile unsigned long *p, unsigned long old, unsigned long new)
        unsigned long prev;
 
        __asm__ __volatile__ (
-       PPC_RELEASE_BARRIER
+       PPC_ATOMIC_ENTRY_BARRIER
 "1:    ldarx   %0,0,%2         # __cmpxchg_u64\n\
        cmpd    0,%0,%3\n\
        bne-    2f\n\
        stdcx.  %4,0,%2\n\
        bne-    1b"
-       PPC_ACQUIRE_BARRIER
+       PPC_ATOMIC_EXIT_BARRIER
        "\n\
 2:"
        : "=&r" (prev), "+m" (*p)