Messages in this thread Patch in this message |  | | From | Roman Penyaev <> | Subject | [PATCH 2/3] epoll: ep->wq can be woken up unlocked in certain cases | Date | Mon, 3 Feb 2020 21:59:06 +0100 |
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Now ep->lock is responsible for wqueue serialization, thus if ep->lock is taken on write path, wake_up_locked() can be invoked.
Signed-off-by: Roman Penyaev <rpenyaev@suse.de> Cc: Max Neunhoeffer <max@arangodb.com> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Christopher Kohlhoff <chris.kohlhoff@clearpool.io> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Jason Baron <jbaron@akamai.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- 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); if (waitqueue_active(&ep->poll_wait)) pwake++; } @@ -1657,7 +1663,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, /* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) - wake_up(&ep->wq); + wake_up_locked(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } -- 2.24.1
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