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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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