提交 a9668cd6 编写于 作者: P Peter Zijlstra 提交者: Ingo Molnar

locking: Remove smp_mb__before_spinlock()

Now that there are no users of smp_mb__before_spinlock() left, remove
it entirely.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
上级 d89e588c
......@@ -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:
......
......@@ -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:
......
......@@ -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()
......
......@@ -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 */
......@@ -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;
}
......
......@@ -117,19 +117,6 @@ do { \
#endif /*arch_spin_is_contended*/
#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:
*
......
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