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authorPeter Zijlstra <peterz@infradead.org>2017-02-01 18:39:38 +0300
committerIngo Molnar <mingo@kernel.org>2017-03-23 10:54:40 +0300
commita9ebf306f52c756c4f9e50ee9a60cd6389d71344 (patch)
treeb1637bcffdc85d3e6e49858a8de5de3ba4ef2f7d /include/linux/atomic.h
parentbf7b3ac2e36ac054f93e5dd8d85dfd754b5e1c09 (diff)
downloadlinux-a9ebf306f52c756c4f9e50ee9a60cd6389d71344.tar.xz
locking/atomic: Introduce atomic_try_cmpxchg()
Add a new cmpxchg interface: bool try_cmpxchg(u{8,16,32,64} *ptr, u{8,16,32,64} *val, u{8,16,32,64} new); Where the boolean returns the result of the compare; and thus if the exchange happened; and in case of failure, the new value of *ptr is returned in *val. This allows simplification/improvement of loops like: for (;;) { new = val $op $imm; old = cmpxchg(ptr, val, new); if (old == val) break; val = old; } into: do { } while (!try_cmpxchg(ptr, &val, val $op $imm)); while also generating better code (GCC6 and onwards). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/atomic.h')
-rw-r--r--include/linux/atomic.h42
1 files changed, 42 insertions, 0 deletions
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index e71835bf60a9..aae5953817d6 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -423,6 +423,27 @@
#endif
#endif /* atomic_cmpxchg_relaxed */
+#ifndef atomic_try_cmpxchg
+
+#define __atomic_try_cmpxchg(type, _p, _po, _n) \
+({ \
+ typeof(_po) __po = (_po); \
+ typeof(*(_po)) __o = *__po; \
+ *__po = atomic_cmpxchg##type((_p), __o, (_n)); \
+ (*__po == __o); \
+})
+
+#define atomic_try_cmpxchg(_p, _po, _n) __atomic_try_cmpxchg(, _p, _po, _n)
+#define atomic_try_cmpxchg_relaxed(_p, _po, _n) __atomic_try_cmpxchg(_relaxed, _p, _po, _n)
+#define atomic_try_cmpxchg_acquire(_p, _po, _n) __atomic_try_cmpxchg(_acquire, _p, _po, _n)
+#define atomic_try_cmpxchg_release(_p, _po, _n) __atomic_try_cmpxchg(_release, _p, _po, _n)
+
+#else /* atomic_try_cmpxchg */
+#define atomic_try_cmpxchg_relaxed atomic_try_cmpxchg
+#define atomic_try_cmpxchg_acquire atomic_try_cmpxchg
+#define atomic_try_cmpxchg_release atomic_try_cmpxchg
+#endif /* atomic_try_cmpxchg */
+
/* cmpxchg_relaxed */
#ifndef cmpxchg_relaxed
#define cmpxchg_relaxed cmpxchg
@@ -996,6 +1017,27 @@ static inline int atomic_dec_if_positive(atomic_t *v)
#endif
#endif /* atomic64_cmpxchg_relaxed */
+#ifndef atomic64_try_cmpxchg
+
+#define __atomic64_try_cmpxchg(type, _p, _po, _n) \
+({ \
+ typeof(_po) __po = (_po); \
+ typeof(*(_po)) __o = *__po; \
+ *__po = atomic64_cmpxchg##type((_p), __o, (_n)); \
+ (*__po == __o); \
+})
+
+#define atomic64_try_cmpxchg(_p, _po, _n) __atomic64_try_cmpxchg(, _p, _po, _n)
+#define atomic64_try_cmpxchg_relaxed(_p, _po, _n) __atomic64_try_cmpxchg(_relaxed, _p, _po, _n)
+#define atomic64_try_cmpxchg_acquire(_p, _po, _n) __atomic64_try_cmpxchg(_acquire, _p, _po, _n)
+#define atomic64_try_cmpxchg_release(_p, _po, _n) __atomic64_try_cmpxchg(_release, _p, _po, _n)
+
+#else /* atomic64_try_cmpxchg */
+#define atomic64_try_cmpxchg_relaxed atomic64_try_cmpxchg
+#define atomic64_try_cmpxchg_acquire atomic64_try_cmpxchg
+#define atomic64_try_cmpxchg_release atomic64_try_cmpxchg
+#endif /* atomic64_try_cmpxchg */
+
#ifndef atomic64_andnot
static inline void atomic64_andnot(long long i, atomic64_t *v)
{