epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events 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>

1 files changed, 87 insertions, 3 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index c0b3c70ee87a..2cf0f2153be5 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