Commit-ID: a9668cd6ee288c4838bc668880ac085be551cac2
Gitweb: http://git.kernel.org/tip/a9668cd6ee288c4838bc668880ac085be551cac2
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 7 Jun 2017 17:51:27 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 10 Aug 2017 12:29:03 +0200
locking: Remove smp_mb__before_spinlock()
Now that there are no users of smp_mb__before_spinlock() left, remove
it entirely.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
Documentation/memory-barriers.txt | 5 +----
.../translations/ko_KR/memory-barriers.txt | 5 +----
arch/arm64/include/asm/spinlock.h | 9 --------
arch/powerpc/include/asm/barrier.h | 7 ------
fs/userfaultfd.c | 25 ++++++++++------------
include/linux/spinlock.h | 13 -----------
6 files changed, 13 insertions(+), 51 deletions(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 9f34364..d1d1716 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1981,10 +1981,7 @@ for each construct. These operations all imply certain barriers:
ACQUIRE operation has completed.
Memory operations issued before the ACQUIRE may be completed after
- the ACQUIRE operation has completed. An smp_mb__before_spinlock(),
- combined with a following ACQUIRE, orders prior stores against
- subsequent loads and stores. Note that this is weaker than smp_mb()!
- The smp_mb__before_spinlock() primitive is free on many architectures.
+ the ACQUIRE operation has completed.
(2) RELEASE operation implication:
diff --git a/Documentation/translations/ko_KR/memory-barriers.txt b/Documentation/translations/ko_KR/memory-barriers.txt
index 38310dc..bc80fc0 100644
--- a/Documentation/translations/ko_KR/memory-barriers.txt
+++ b/Documentation/translations/ko_KR/memory-barriers.txt
@@ -1956,10 +1956,7 @@ MMIO 쓰기 배리어
뒤에 완료됩니다.
ACQUIRE 앞에서 요청된 메모리 오퍼레이션은 ACQUIRE 오퍼레이션이 완료된 후에
- 완료될 수 있습니다. smp_mb__before_spinlock() 뒤에 ACQUIRE 가 실행되는
- 코드 블록은 블록 앞의 스토어를 블록 뒤의 로드와 스토어에 대해 순서
- 맞춥니다. 이건 smp_mb() 보다 완화된 것임을 기억하세요! 많은 아키텍쳐에서
- smp_mb__before_spinlock() 은 사실 아무일도 하지 않습니다.
+ 완료될 수 있습니다.
(2) RELEASE 오퍼레이션의 영향:
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index b103888..ae4241a 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -358,15 +358,6 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
#define arch_read_relax(lock) cpu_relax()
#define arch_write_relax(lock) cpu_relax()
-/*
- * Accesses appearing in program order before a spin_lock() operation
- * can be reordered with accesses inside the critical section, by virtue
- * of arch_spin_lock being constructed using acquire semantics.
- *
- * In cases where this is problematic (e.g. try_to_wake_up), an
- * smp_mb__before_spinlock() can restore the required ordering.
- */
-#define smp_mb__before_spinlock() smp_mb()
/* See include/linux/spinlock.h */
#define smp_mb__after_spinlock() smp_mb()
diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index 25d42bd..9c601ad 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -74,13 +74,6 @@ do { \
___p1; \
})
-/*
- * This must resolve to hwsync on SMP for the context switch path.
- * See _switch, and core scheduler context switch memory ordering
- * comments.
- */
-#define smp_mb__before_spinlock() smp_mb()
-
#include <asm-generic/barrier.h>
#endif /* _ASM_POWERPC_BARRIER_H */
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 06ea26b..44fcbef 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -109,27 +109,24 @@ static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
goto out;
WRITE_ONCE(uwq->waken, true);
/*
- * The implicit smp_mb__before_spinlock in try_to_wake_up()
- * renders uwq->waken visible to other CPUs before the task is
- * waken.
+ * The Program-Order guarantees provided by the scheduler
+ * ensure uwq->waken is visible before the task is woken.
*/
ret = wake_up_state(wq->private, mode);
- if (ret)
+ if (ret) {
/*
* Wake only once, autoremove behavior.
*
- * After the effect of list_del_init is visible to the
- * other CPUs, the waitqueue may disappear from under
- * us, see the !list_empty_careful() in
- * handle_userfault(). try_to_wake_up() has an
- * implicit smp_mb__before_spinlock, and the
- * wq->private is read before calling the extern
- * function "wake_up_state" (which in turns calls
- * try_to_wake_up). While the spin_lock;spin_unlock;
- * wouldn't be enough, the smp_mb__before_spinlock is
- * enough to avoid an explicit smp_mb() here.
+ * After the effect of list_del_init is visible to the other
+ * CPUs, the waitqueue may disappear from under us, see the
+ * !list_empty_careful() in handle_userfault().
+ *
+ * try_to_wake_up() has an implicit smp_mb(), and the
+ * wq->private is read before calling the extern function
+ * "wake_up_state" (which in turns calls try_to_wake_up).
*/
list_del_init(&wq->entry);
+ }
out:
return ret;
}
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 8402810..4e8cce1 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -118,19 +118,6 @@ do { \
#endif
/*
- * Despite its name it doesn't necessarily has to be a full barrier.
- * It should only guarantee that a STORE before the critical section
- * can not be reordered with LOADs and STOREs inside this section.
- * spin_lock() is the one-way barrier, this LOAD can not escape out
- * of the region. So the default implementation simply ensures that
- * a STORE can not move into the critical section, smp_wmb() should
- * serialize it with another STORE done by spin_lock().
- */
-#ifndef smp_mb__before_spinlock
-#define smp_mb__before_spinlock() smp_wmb()
-#endif
-
-/*
* This barrier must provide two things:
*
* - it must guarantee a STORE before the spin_lock() is ordered against a
--
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