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author | Dan Williams <dan.j.williams@intel.com> | 2017-11-15 16:56:11 -0800 |
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committer | Dan Williams <dan.j.williams@intel.com> | 2017-11-15 16:56:11 -0800 |
commit | 4247f24c23589bcc3bc3490515ef8c9497e9ae55 (patch) | |
tree | 89726a0e171c443a3e8def2992b56dbd8a21df21 /kernel/locking/rwsem-xadd.c | |
parent | 79ab67ede21f536851a99ea68ee6fc1f5435e055 (diff) | |
parent | 9f586fff6574f6ecbf323f92d44ffaf0d96225fe (diff) |
Merge branch 'for-4.15/dax' into libnvdimm-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 |