Commit 57804b1c authored by Al Viro's avatar Al Viro
Browse files

lift locking/unlocking ep->mtx out of ep_{start,done}_scan() 



get rid of depth/ep_locked arguments there and document
the kludge in ep_item_poll() that has lead to ep_locked existence in
the first place

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ff07952a

fs/eventpoll.c

+26 −31
Original line number Diff line number Diff line
@@ -554,20 +554,13 @@ static inline void ep_pm_stay_awake_rcu(struct epitem *epi) 
	rcu_read_unlock();

}



static void ep_start_scan(struct eventpoll *ep,

			  int depth, bool ep_locked,

			  struct list_head *txlist)

{

	lockdep_assert_irqs_enabled();



/*

	 * We need to lock this because we could be hit by

 * ep->mutex needs to be held because we could be hit by

 * eventpoll_release_file() and epoll_ctl().

 */



	if (!ep_locked)

		mutex_lock_nested(&ep->mtx, depth);



static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist)

{

	/*

	 * Steal the ready list, and re-init the original one to the

	 * empty list. Also, set ep->ovflist to NULL so that events
@@ -576,6 +569,7 @@ static void ep_start_scan(struct eventpoll *ep, 
	 * because we want the "sproc" callback to be able to do it

	 * in a lockless way.

	 */

	lockdep_assert_irqs_enabled();

	write_lock_irq(&ep->lock);

	list_splice_init(&ep->rdllist, txlist);

	WRITE_ONCE(ep->ovflist, NULL);
@@ -583,7 +577,6 @@ static void ep_start_scan(struct eventpoll *ep, 
}



static void ep_done_scan(struct eventpoll *ep,

			 int depth, bool ep_locked,

			 struct list_head *txlist)

{

	struct epitem *epi, *nepi;
@@ -624,9 +617,6 @@ static void ep_done_scan(struct eventpoll *ep, 
	list_splice(txlist, &ep->rdllist);

	__pm_relax(ep->ws);

	write_unlock_irq(&ep->lock);



	if (!ep_locked)

		mutex_unlock(&ep->mtx);

}



static void epi_rcu_free(struct rcu_head *head)
@@ -763,11 +753,16 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, 


	ep = epi->ffd.file->private_data;

	poll_wait(epi->ffd.file, &ep->poll_wait, pt);

	locked = pt && (pt->_qproc == ep_ptable_queue_proc);



	ep_start_scan(ep, depth, locked, &txlist);

	// kludge: ep_insert() calls us with ep->mtx already locked

	locked = pt && (pt->_qproc == ep_ptable_queue_proc);

	if (!locked)

		mutex_lock_nested(&ep->mtx, depth);

	ep_start_scan(ep, &txlist);

	res = ep_read_events_proc(ep, &txlist, depth + 1);

	ep_done_scan(ep, depth, locked, &txlist);

	ep_done_scan(ep, &txlist);

	if (!locked)

		mutex_unlock(&ep->mtx);

	return res & epi->event.events;

}
@@ -809,9 +804,11 @@ static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) 
	 * Proceed to find out if wanted events are really available inside

	 * the ready list.

	 */

	ep_start_scan(ep, 0, false, &txlist);

	mutex_lock(&ep->mtx);

	ep_start_scan(ep, &txlist);

	res = ep_read_events_proc(ep, &txlist, 1);

	ep_done_scan(ep, 0, false, &txlist);

	ep_done_scan(ep, &txlist);

	mutex_unlock(&ep->mtx);

	return res;

}
@@ -1573,15 +1570,13 @@ static int ep_send_events(struct eventpoll *ep, 


	init_poll_funcptr(&pt, NULL);



	ep_start_scan(ep, 0, false, &txlist);

	mutex_lock(&ep->mtx);

	ep_start_scan(ep, &txlist);



	/*

	 * We can loop without lock because we are passed a task private list.

	 * Items cannot vanish during the loop because ep_scan_ready_list() is

	 * holding "mtx" during this call.

	 * Items cannot vanish during the loop we are holding ep->mtx.

	 */

	lockdep_assert_held(&ep->mtx);



	list_for_each_entry_safe(epi, tmp, &txlist, rdllink) {

		struct wakeup_source *ws;

		__poll_t revents;
@@ -1609,9 +1604,8 @@ static int ep_send_events(struct eventpoll *ep, 


		/*

		 * If the event mask intersect the caller-requested one,

		 * deliver the event to userspace. Again, ep_scan_ready_list()

		 * is holding ep->mtx, so no operations coming from userspace

		 * can change the item.

		 * deliver the event to userspace. Again, we are holding ep->mtx,

		 * so no operations coming from userspace can change the item.

		 */

		revents = ep_item_poll(epi, &pt, 1);

		if (!revents)
@@ -1645,7 +1639,8 @@ static int ep_send_events(struct eventpoll *ep, 
			ep_pm_stay_awake(epi);

		}

	}

	ep_done_scan(ep, 0, false, &txlist);

	ep_done_scan(ep, &txlist);

	mutex_unlock(&ep->mtx);



	return res;

}