[PATCH 2/5][Bionic][SRU Artful] locking/atomic: Add atomic_cond_read_acquire()

[dann frazier]

From: Will Deacon <will.deacon at arm.com>

BugLink: https://bugs.launchpad.net/bugs/1732238

smp_cond_load_acquire() provides a way to spin on a variable with acquire
semantics until some conditional expression involving the variable is
satisfied. Architectures such as arm64 can potentially enter a low-power
state, waking up only when the value of the variable changes, which
reduces the system impact of tight polling loops.

This patch makes the same interface available to users of atomic_t,
atomic64_t and atomic_long_t, rather than require messy accesses to the
structure internals.

Signed-off-by: Will Deacon <will.deacon at arm.com>
Acked-by: Peter Zijlstra <peterz at infradead.org>
Cc: Boqun Feng <boqun.feng at gmail.com>
Cc: Jeremy.Linton at arm.com
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Waiman Long <longman at redhat.com>
Cc: linux-arm-kernel at lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-3-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
(cherry picked from commit 4df714be4dcf40bfb0d4af0f851a6e1977afa02e)
Signed-off-by: dann frazier <dann.frazier at canonical.com>
---
 include/asm-generic/atomic-long.h | 3 +++
 include/linux/atomic.h            | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/include/asm-generic/atomic-long.h b/include/asm-generic/atomic-long.h
index 288cc9e96395..f2d97b782031 100644
--- a/include/asm-generic/atomic-long.h
+++ b/include/asm-generic/atomic-long.h
@@ -243,4 +243,7 @@ static inline long atomic_long_add_unless(atomic_long_t *l, long a, long u)
 #define atomic_long_inc_not_zero(l) \
 	ATOMIC_LONG_PFX(_inc_not_zero)((ATOMIC_LONG_PFX(_t) *)(l))
 
+#define atomic_long_cond_read_acquire(v, c) \
+	ATOMIC_LONG_PFX(_cond_read_acquire)((ATOMIC_LONG_PFX(_t) *)(v), (c))
+
 #endif  /*  _ASM_GENERIC_ATOMIC_LONG_H  */
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index c56be7410130..b848b91c3137 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -650,6 +650,8 @@ static inline int atomic_dec_if_positive(atomic_t *v)
 }
 #endif
 
+#define atomic_cond_read_acquire(v, c)	smp_cond_load_acquire(&(v)->counter, (c))
+
 #ifdef CONFIG_GENERIC_ATOMIC64
 #include <asm-generic/atomic64.h>
 #endif
@@ -1069,6 +1071,8 @@ static inline long long atomic64_fetch_andnot_release(long long i, atomic64_t *v
 }
 #endif
 
+#define atomic64_cond_read_acquire(v, c)	smp_cond_load_acquire(&(v)->counter, (c))
+
 #include <asm-generic/atomic-long.h>
 
 #endif /* _LINUX_ATOMIC_H */
-- 
2.15.1