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author | Takashi Iwai <tiwai@suse.de> | 2017-10-05 15:08:57 +0200 |
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committer | Takashi Iwai <tiwai@suse.de> | 2017-10-05 15:08:57 +0200 |
commit | 3a9fce327ff9cabf7f89d3f20616a83af28393da (patch) | |
tree | c516d3e7023e7fe2dc8d4cf60e2ec03f3c9b5958 /kernel/locking/rwsem-xadd.c | |
parent | e195a331c4124a6527e5e1b6fbd93a6b4a984d7b (diff) | |
parent | 394ca81cb4c1518e9463fe342fb1ae8a9f46a82d (diff) |
Merge branch 'topic/timer-api' into for-next
Diffstat (limited to 'kernel/locking/rwsem-xadd.c')
-rw-r--r-- | kernel/locking/rwsem-xadd.c | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 02f660666ab8..1fefe6dcafd7 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -613,6 +613,33 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) DEFINE_WAKE_Q(wake_q); /* + * __rwsem_down_write_failed_common(sem) + * rwsem_optimistic_spin(sem) + * osq_unlock(sem->osq) + * ... + * atomic_long_add_return(&sem->count) + * + * - VS - + * + * __up_write() + * if (atomic_long_sub_return_release(&sem->count) < 0) + * rwsem_wake(sem) + * osq_is_locked(&sem->osq) + * + * And __up_write() must observe !osq_is_locked() when it observes the + * atomic_long_add_return() in order to not miss a wakeup. + * + * This boils down to: + * + * [S.rel] X = 1 [RmW] r0 = (Y += 0) + * MB RMB + * [RmW] Y += 1 [L] r1 = X + * + * exists (r0=1 /\ r1=0) + */ + smp_rmb(); + + /* * If a spinner is present, it is not necessary to do the wakeup. * Try to do wakeup only if the trylock succeeds to minimize * spinlock contention which may introduce too much delay in the |