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Commit 86c05179 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
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fs/epoll: deal with wait_queue only once 

There is no reason why we rearm the waitiqueue upon every fetch_events
retry (for when events are found yet send_events() fails).  If nothing
else, this saves four lock operations per retry, and furthermore reduces
the scope of the lock even further.

[akpm@linux-foundation.org: restore code to original position, fix and reflow comment]
Link: http://lkml.kernel.org/r/20181114182532.27981-2-dave@stgolabs.net


Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 35cff1a6

fs/eventpoll.c

+18 −11
Original line number Diff line number Diff line
@@ -1749,6 +1749,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
{

	int res = 0, eavail, timed_out = 0;

	u64 slack = 0;

	bool waiter = false;

	wait_queue_entry_t wait;

	ktime_t expires, *to = NULL;
@@ -1794,14 +1795,18 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
	ep_reset_busy_poll_napi_id(ep);



	/*

	 * We don't have any available event to return to the caller.

	 * We need to sleep here, and we will be wake up by

	 * ep_poll_callback() when events will become available.

	 * We don't have any available event to return to the caller.  We need

	 * to sleep here, and we will be woken by ep_poll_callback() when events

	 * become available.

	 */

	if (!waiter) {

		waiter = true;

		init_waitqueue_entry(&wait, current);



		spin_lock_irq(&ep->wq.lock);

		__add_wait_queue_exclusive(&ep->wq, &wait);

		spin_unlock_irq(&ep->wq.lock);

	}



	for (;;) {

		/*
@@ -1837,10 +1842,6 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 


	__set_current_state(TASK_RUNNING);



	spin_lock_irq(&ep->wq.lock);

	__remove_wait_queue(&ep->wq, &wait);

	spin_unlock_irq(&ep->wq.lock);



send_events:

	/*

	 * Try to transfer events to user space. In case we get 0 events and
@@ -1851,6 +1852,12 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
	    !(res = ep_send_events(ep, events, maxevents)) && !timed_out)

		goto fetch_events;



	if (waiter) {

		spin_lock_irq(&ep->wq.lock);

		__remove_wait_queue(&ep->wq, &wait);

		spin_unlock_irq(&ep->wq.lock);

	}



	return res;

}