From 4d7e30d98939a0340022ccd49325a3d70f7e0238 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Arve=20Hj=C3=B8nnev=C3=A5g?= Date: Tue, 1 May 2012 21:33:34 +0200 Subject: [PATCH] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: NeilBrown Signed-off-by: Rafael J. Wysocki --- 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 c0b3c70ee87..2cf0f2153be 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -33,6 +33,7 @@ #include #include #include +#include #include #include #include @@ -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 12d52dedb22..c398cff3dab 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 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 657ab55beda..6f8be328770 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 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) -- 2.20.1