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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: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2020-08-31 13:41:30 -04:00
parent ff07952aed
commit 57804b1cc4
1 changed files with 26 additions and 31 deletions
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57
fs/eventpoll.c
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@ -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)
/*
* ep->mutex needs to be held because we could be hit by
* eventpoll_release_file() and epoll_ctl().
*/
static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist)
{
lockdep_assert_irqs_enabled();
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() and epoll_ctl().
*/
if (!ep_locked)
mutex_lock_nested(&ep->mtx, depth);
/*
* 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;
}