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Subject[PATCH] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready
Date
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>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
fs/eventpoll.c | 90 ++++++++++++++++++++++++++++++++++++++++++-
include/linux/capability.h | 5 ++-
include/linux/eventpoll.h | 12 ++++++
3 files changed, 103 insertions(+), 4 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 739b098..1abed50 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -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>
@@ -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
@@ -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;
};
@@ -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;

@@ -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
@@ -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)) {
/*
@@ -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);

@@ -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);
}

@@ -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);
}
}
@@ -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()
@@ -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.
*/
@@ -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;
@@ -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))
@@ -1204,6 +1260,9 @@ error_unregister:
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;
@@ -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
@@ -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))
@@ -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;
@@ -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++;
@@ -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);
}
}
}
@@ -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
diff --git a/include/linux/capability.h b/include/linux/capability.h
index 12d52de..222974a 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -360,8 +360,11 @@ struct cpu_vfs_cap_data {

#define CAP_WAKE_ALARM 35

+/* Allow preventing automatic 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)

diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 657ab55..5b591fb 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -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 automatic
+ * system suspends from happening while those events are being processed.
+ *
+ * Assuming neither EPOLLET nor EPOLLONESHOT is set, automatic 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)

--
1.7.7.3
--
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