On 2/10/20 4:41 AM, Roman Penyaev wrote: > Now ep->lock is responsible for wqueue serialization, thus if ep->lock > is taken on write path, wake_up_locked() can be invoked. > > Though, read path is different. Since concurrent cpus can enter the > wake up function it needs to be internally serialized, thus wake_up() > variant is used which implies internal spin lock. > > Signed-off-by: Roman Penyaev <rpenyaev@xxxxxxx> > Cc: Max Neunhoeffer <max@xxxxxxxxxxxx> > Cc: Jakub Kicinski <kuba@xxxxxxxxxx> > Cc: Christopher Kohlhoff <chris.kohlhoff@xxxxxxxxxxxx> > Cc: Davidlohr Bueso <dbueso@xxxxxxx> > Cc: Jason Baron <jbaron@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- > Nothing interesting in v2: > changed the comment a bit > > fs/eventpoll.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/eventpoll.c b/fs/eventpoll.c > index eee3c92a9ebf..6e218234bd4a 100644 > --- a/fs/eventpoll.c > +++ b/fs/eventpoll.c > @@ -1173,7 +1173,7 @@ static inline bool chain_epi_lockless(struct epitem *epi) > * Another thing worth to mention is that ep_poll_callback() can be called > * concurrently for the same @epi from different CPUs if poll table was inited > * with several wait queues entries. Plural wakeup from different CPUs of a > - * single wait queue is serialized by wq.lock, but the case when multiple wait > + * single wait queue is serialized by ep->lock, but the case when multiple wait > * queues are used should be detected accordingly. This is detected using > * cmpxchg() operation. > */ > @@ -1248,6 +1248,12 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v > break; > } > } > + /* > + * Since here we have the read lock (ep->lock) taken, plural > + * wakeup from different CPUs can occur, thus we call wake_up() > + * variant which implies its own lock on wqueue. All other paths > + * take write lock. > + */ > wake_up(&ep->wq); > } > if (waitqueue_active(&ep->poll_wait)) > @@ -1551,7 +1557,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, > > /* Notify waiting tasks that events are available */ > if (waitqueue_active(&ep->wq)) > - wake_up(&ep->wq); > + wake_up_locked(&ep->wq); So I think this will now hit the 'lockdep_assert_held()' in __wake_up_common()? I agree that its correct, but I think it will confuse lockdep here... Thanks, -Jason
