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epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events…
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… are ready

When an epoll_event, that has the EPOLLWAKEUP flag set, is ready, a
wakeup_source will be active to prevent suspend. This can be used to
handle wakeup events from a driver that support poll, e.g. input, if
that driver wakes up the waitqueue passed to epoll before allowing
suspend.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
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Arve Hjønnevåg authored and Rafael J. Wysocki committed May 5, 2012
1 parent b86ff98 commit 4d7e30d
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Showing 3 changed files with 103 additions and 4 deletions.
90 changes: 87 additions & 3 deletions fs/eventpoll.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/anon_inodes.h>
#include <linux/device.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/mman.h>
Expand Down Expand Up @@ -87,7 +88,7 @@
*/

/* Epoll private bits inside the event mask */
#define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)
#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET)

/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4
Expand Down Expand Up @@ -154,6 +155,9 @@ struct epitem {
/* List header used to link this item to the "struct file" items list */
struct list_head fllink;

/* wakeup_source used when EPOLLWAKEUP is set */
struct wakeup_source *ws;

/* The structure that describe the interested events and the source fd */
struct epoll_event event;
};
Expand Down Expand Up @@ -194,6 +198,9 @@ struct eventpoll {
*/
struct epitem *ovflist;

/* wakeup_source used when ep_scan_ready_list is running */
struct wakeup_source *ws;

/* The user that created the eventpoll descriptor */
struct user_struct *user;

Expand Down Expand Up @@ -588,8 +595,10 @@ static int ep_scan_ready_list(struct eventpoll *ep,
* queued into ->ovflist but the "txlist" might already
* contain them, and the list_splice() below takes care of them.
*/
if (!ep_is_linked(&epi->rdllink))
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
}
}
/*
* We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
Expand All @@ -602,6 +611,7 @@ static int ep_scan_ready_list(struct eventpoll *ep,
* Quickly re-inject items left on "txlist".
*/
list_splice(&txlist, &ep->rdllist);
__pm_relax(ep->ws);

if (!list_empty(&ep->rdllist)) {
/*
Expand Down Expand Up @@ -656,6 +666,8 @@ 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);

/* At this point it is safe to free the eventpoll item */
kmem_cache_free(epi_cache, epi);

Expand Down Expand Up @@ -706,6 +718,7 @@ static void ep_free(struct eventpoll *ep)
mutex_unlock(&epmutex);
mutex_destroy(&ep->mtx);
free_uid(ep->user);
wakeup_source_unregister(ep->ws);
kfree(ep);
}

Expand Down Expand Up @@ -737,6 +750,7 @@ 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);
list_del_init(&epi->rdllink);
}
}
Expand Down Expand Up @@ -927,13 +941,23 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
if (epi->next == EP_UNACTIVE_PTR) {
epi->next = ep->ovflist;
ep->ovflist = epi;
if (epi->ws) {
/*
* Activate ep->ws since epi->ws may get
* deactivated at any time.
*/
__pm_stay_awake(ep->ws);
}

}
goto out_unlock;
}

/* If this file is already in the ready list we exit soon */
if (!ep_is_linked(&epi->rdllink))
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
__pm_stay_awake(epi->ws);
}

/*
* Wake up ( if active ) both the eventpoll wait list and the ->poll()
Expand Down Expand Up @@ -1091,6 +1115,30 @@ static int reverse_path_check(void)
return error;
}

static int ep_create_wakeup_source(struct epitem *epi)
{
const char *name;

if (!epi->ep->ws) {
epi->ep->ws = wakeup_source_register("eventpoll");
if (!epi->ep->ws)
return -ENOMEM;
}

name = epi->ffd.file->f_path.dentry->d_name.name;
epi->ws = wakeup_source_register(name);
if (!epi->ws)
return -ENOMEM;

return 0;
}

static void ep_destroy_wakeup_source(struct epitem *epi)
{
wakeup_source_unregister(epi->ws);
epi->ws = NULL;
}

/*
* Must be called with "mtx" held.
*/
Expand Down Expand Up @@ -1118,6 +1166,13 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
epi->event = *event;
epi->nwait = 0;
epi->next = EP_UNACTIVE_PTR;
if (epi->event.events & EPOLLWAKEUP) {
error = ep_create_wakeup_source(epi);
if (error)
goto error_create_wakeup_source;
} else {
epi->ws = NULL;
}

/* Initialize the poll table using the queue callback */
epq.epi = epi;
Expand Down Expand Up @@ -1164,6 +1219,7 @@ 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);

/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
Expand Down Expand Up @@ -1204,6 +1260,9 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
list_del_init(&epi->rdllink);
spin_unlock_irqrestore(&ep->lock, flags);

wakeup_source_unregister(epi->ws);

error_create_wakeup_source:
kmem_cache_free(epi_cache, epi);

return error;
Expand All @@ -1229,6 +1288,12 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
epi->event.events = event->events;
pt._key = event->events;
epi->event.data = event->data; /* protected by mtx */
if (epi->event.events & EPOLLWAKEUP) {
if (!epi->ws)
ep_create_wakeup_source(epi);
} else if (epi->ws) {
ep_destroy_wakeup_source(epi);
}

/*
* Get current event bits. We can safely use the file* here because
Expand All @@ -1244,6 +1309,7 @@ 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);

/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
Expand Down Expand Up @@ -1282,6 +1348,18 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
!list_empty(head) && eventcnt < esed->maxevents;) {
epi = list_first_entry(head, struct epitem, rdllink);

/*
* Activate ep->ws before deactivating epi->ws to prevent
* triggering auto-suspend here (in case we reactive epi->ws
* below).
*
* This could be rearranged to delay the deactivation of epi->ws
* 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);
list_del_init(&epi->rdllink);

pt._key = epi->event.events;
Expand All @@ -1298,6 +1376,7 @@ 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);
return eventcnt ? eventcnt : -EFAULT;
}
eventcnt++;
Expand All @@ -1317,6 +1396,7 @@ 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);
}
}
}
Expand Down Expand Up @@ -1629,6 +1709,10 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
if (!tfile->f_op || !tfile->f_op->poll)
goto error_tgt_fput;

/* Check if EPOLLWAKEUP is allowed */
if ((epds.events & EPOLLWAKEUP) && !capable(CAP_EPOLLWAKEUP))
goto error_tgt_fput;

/*
* We have to check that the file structure underneath the file descriptor
* the user passed to us _is_ an eventpoll file. And also we do not permit
Expand Down
5 changes: 4 additions & 1 deletion include/linux/capability.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -360,8 +360,11 @@ struct cpu_vfs_cap_data {

#define CAP_WAKE_ALARM 35

/* Allow preventing system suspends while epoll events are pending */

#define CAP_LAST_CAP CAP_WAKE_ALARM
#define CAP_EPOLLWAKEUP 36

#define CAP_LAST_CAP CAP_EPOLLWAKEUP

#define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)

Expand Down
12 changes: 12 additions & 0 deletions include/linux/eventpoll.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,18 @@
#define EPOLL_CTL_DEL 2
#define EPOLL_CTL_MOD 3

/*
* Request the handling of system wakeup events so as to prevent system suspends
* from happening while those events are being processed.
*
* Assuming neither EPOLLET nor EPOLLONESHOT is set, system suspends will not be
* re-allowed until epoll_wait is called again after consuming the wakeup
* event(s).
*
* Requires CAP_EPOLLWAKEUP
*/
#define EPOLLWAKEUP (1 << 29)

/* Set the One Shot behaviour for the target file descriptor */
#define EPOLLONESHOT (1 << 30)

Expand Down

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