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-rw-r--r--arch/x86/lib/atomic64_32.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/arch/x86/lib/atomic64_32.c b/arch/x86/lib/atomic64_32.c
index 5fc1e2caa544..61959627e1e1 100644
--- a/arch/x86/lib/atomic64_32.c
+++ b/arch/x86/lib/atomic64_32.c
@@ -76,13 +76,22 @@ u64 atomic64_read(atomic64_t *ptr)
76 */ 76 */
77u64 atomic64_add_return(u64 delta, atomic64_t *ptr) 77u64 atomic64_add_return(u64 delta, atomic64_t *ptr)
78{ 78{
79 u64 old_val, new_val; 79 /*
80 * Try first with a (probably incorrect) assumption about
81 * what we have there. We'll do two loops most likely,
82 * but we'll get an ownership MESI transaction straight away
83 * instead of a read transaction followed by a
84 * flush-for-ownership transaction:
85 */
86 u64 old_val, new_val, real_val = 1ULL << 32;
80 87
81 do { 88 do {
82 old_val = atomic_read(ptr); 89 old_val = real_val;
83 new_val = old_val + delta; 90 new_val = old_val + delta;
84 91
85 } while (atomic64_cmpxchg(ptr, old_val, new_val) != old_val); 92 real_val = atomic64_cmpxchg(ptr, old_val, new_val);
93
94 } while (real_val != old_val);
86 95
87 return new_val; 96 return new_val;
88} 97}