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epoll: use RCU to protect wakeup_source in epitem 

This prevents wakeup_source destruction when a user hits the item with
EPOLL_CTL_MOD while ep_poll_callback is running.

Tested with CONFIG_SPARSE_RCU_POINTER=y and "make fs/eventpoll.o C=2"

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: NeilBrown <neilb@suse.de>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Wong 2013-04-30 15:27:39 -07:00 committed by Linus Torvalds
parent 39732ca5af
commit eea1d58591
1 changed files with 71 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
fs/eventpoll.c
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@ -160,7 +160,7 @@ struct epitem {
struct list_head fllink;
/* wakeup_source used when EPOLLWAKEUP is set */
struct wakeup_source *ws;
struct wakeup_source __rcu *ws;
/* The structure that describe the interested events and the source fd */
struct epoll_event event;
@ -538,6 +538,38 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
}
}
/* call only when ep->mtx is held */
static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
{
return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
}
/* call only when ep->mtx is held */
static inline void ep_pm_stay_awake(struct epitem *epi)
{
struct wakeup_source *ws = ep_wakeup_source(epi);
if (ws)
__pm_stay_awake(ws);
}
static inline bool ep_has_wakeup_source(struct epitem *epi)
{
return rcu_access_pointer(epi->ws) ? true : false;
}
/* call when ep->mtx cannot be held (ep_poll_callback) */
static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
{
struct wakeup_source *ws;
rcu_read_lock();
ws = rcu_dereference(epi->ws);
if (ws)
__pm_stay_awake(ws);
rcu_read_unlock();
}
/**
* ep_scan_ready_list - Scans the ready list in a way that makes possible for
* the scan code, to call f_op->poll(). Also allows for
@ -601,7 +633,7 @@ static int ep_scan_ready_list(struct eventpoll *ep,
*/
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake(epi);
}
}
/*
@ -670,7 +702,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
list_del_init(&epi->rdllink);
spin_unlock_irqrestore(&ep->lock, flags);
wakeup_source_unregister(epi->ws);
wakeup_source_unregister(ep_wakeup_source(epi));
/* At this point it is safe to free the eventpoll item */
kmem_cache_free(epi_cache, epi);
@ -754,7 +786,7 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
* callback, but it's not actually ready, as far as
* caller requested events goes. We can remove it here.
*/
__pm_relax(epi->ws);
__pm_relax(ep_wakeup_source(epi));
list_del_init(&epi->rdllink);
}
}
@ -986,7 +1018,7 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
/* If this file is already in the ready list we exit soon */
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake_rcu(epi);
}
/*
@ -1148,6 +1180,7 @@ static int reverse_path_check(void)
static int ep_create_wakeup_source(struct epitem *epi)
{
const char *name;
struct wakeup_source *ws;
if (!epi->ep->ws) {
epi->ep->ws = wakeup_source_register("eventpoll");
@ -1156,17 +1189,29 @@ static int ep_create_wakeup_source(struct epitem *epi)
}
name = epi->ffd.file->f_path.dentry->d_name.name;
epi->ws = wakeup_source_register(name);
if (!epi->ws)
ws = wakeup_source_register(name);
if (!ws)
return -ENOMEM;
rcu_assign_pointer(epi->ws, ws);
return 0;
}
static void ep_destroy_wakeup_source(struct epitem *epi)
/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
static noinline void ep_destroy_wakeup_source(struct epitem *epi)
{
wakeup_source_unregister(epi->ws);
epi->ws = NULL;
struct wakeup_source *ws = ep_wakeup_source(epi);
rcu_assign_pointer(epi->ws, NULL);
/*
* wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
* used internally by wakeup_source_remove, too (called by
* wakeup_source_unregister), so we cannot use call_rcu
*/
synchronize_rcu();
wakeup_source_unregister(ws);
}
/*
@ -1201,7 +1246,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
if (error)
goto error_create_wakeup_source;
} else {
epi->ws = NULL;
RCU_INIT_POINTER(epi->ws, NULL);
}
/* Initialize the poll table using the queue callback */
@ -1249,7 +1294,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
/* If the file is already "ready" we drop it inside the ready list */
if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
@ -1290,7 +1335,7 @@ error_unregister:
list_del_init(&epi->rdllink);
spin_unlock_irqrestore(&ep->lock, flags);
wakeup_source_unregister(epi->ws);
wakeup_source_unregister(ep_wakeup_source(epi));
error_create_wakeup_source:
kmem_cache_free(epi_cache, epi);
@ -1319,9 +1364,9 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
pt._key = event->events;
epi->event.data = event->data; /* protected by mtx */
if (epi->event.events & EPOLLWAKEUP) {
if (!epi->ws)
if (!ep_has_wakeup_source(epi))
ep_create_wakeup_source(epi);
} else if (epi->ws) {
} else if (ep_has_wakeup_source(epi)) {
ep_destroy_wakeup_source(epi);
}
@ -1359,7 +1404,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
spin_lock_irq(&ep->lock);
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
@ -1385,6 +1430,7 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
unsigned int revents;
struct epitem *epi;
struct epoll_event __user *uevent;
struct wakeup_source *ws;
poll_table pt;
init_poll_funcptr(&pt, NULL);
@ -1407,9 +1453,13 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
* instead, but then epi->ws would temporarily be out of sync
* with ep_is_linked().
*/
if (epi->ws && epi->ws->active)
__pm_stay_awake(ep->ws);
__pm_relax(epi->ws);
ws = ep_wakeup_source(epi);
if (ws) {
if (ws->active)
__pm_stay_awake(ep->ws);
__pm_relax(ws);
}
list_del_init(&epi->rdllink);
pt._key = epi->event.events;
@ -1426,7 +1476,7 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
if (__put_user(revents, &uevent->events) ||
__put_user(epi->event.data, &uevent->data)) {
list_add(&epi->rdllink, head);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake(epi);
return eventcnt ? eventcnt : -EFAULT;
}
eventcnt++;
@ -1446,7 +1496,7 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
* poll callback will queue them in ep->ovflist.
*/
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
ep_pm_stay_awake(epi);
}
}
}