From e8895a983c866ec3261f9881e27a5eeb151cb6b4 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Tue, 5 Nov 2013 16:56:59 +1100 Subject: [PATCH] epoll: remove the on_list check for 'struct epitem' By removing the 'int on_list' field from 'struct epitem', we avoid hitting the BUILD_BUG_ON() for 'struct epitem' being larger than 128 bytes. In file included from include/linux/init.h:4:0, from fs/eventpoll.c:14: fs/eventpoll.c: In function 'eventpoll_init': include/linux/compiler.h:321:20: error: call to '__compiletime_assert_2137' declared with attribute error: BUILD_BUG_ON failed: sizeof(void *) <= 8 && sizeof(struct epitem) > 128 prefix ## suffix(); \ The check to make sure that the 'struct epitem' was actually linked via epi->fllink was added to avoid having the list removal primitives called twice for the same 'struct epitem'. However, the double call possibility was removed by 'Subject: epoll: optimize EPOLL_CTL_DEL using rcu'. There, the call to 'list_del_init()' in eventpoll_release_file() was removed (we now rely on the list delete happening entirely in 'ep_remove()', which is called from eventpoll_release_file()). There is also the question as to whether multiple ep_remove() calls could happen concurrently. This can not happen since EPOLL_CTL_DEL can't race with eventpoll_release_file() or ep_free() - it has to do an fget() to proceed. Further, eventpoll_release_file() can not race with ep_free(), since they both acquire the 'epmutex'. Signed-off-by: Jason Baron Reported-by: Wu Fengguang Cc: Nathan Zimmer Cc: Eric Wong Cc: Nelson Elhage Cc: Al Viro Cc: Davide Libenzi Cc: "Paul E. McKenney" Signed-off-by: Andrew Morton --- fs/eventpoll.c | 13 ++----------- 1 file changed, 2 insertions(+), 11 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 1830b1e89716..584249454822 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -170,9 +170,6 @@ struct epitem { /* The structure that describe the interested events and the source fd */ struct epoll_event event; - - /* The fllink is in use. Since rcu can't do 'list_del_init()' */ - int on_list; }; /* @@ -706,10 +703,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi) /* Remove the current item from the list of epoll hooks */ spin_lock(&file->f_lock); - if (epi->on_list) { - list_del_rcu(&epi->fllink); - epi->on_list = 0; - } + list_del_rcu(&epi->fllink); spin_unlock(&file->f_lock); rb_erase(&epi->rbn, &ep->rbr); @@ -1272,7 +1266,6 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, epi->event = *event; epi->nwait = 0; epi->next = EP_UNACTIVE_PTR; - epi->on_list = 0; if (epi->event.events & EPOLLWAKEUP) { error = ep_create_wakeup_source(epi); if (error) @@ -1306,7 +1299,6 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, /* Add the current item to the list of active epoll hook for this file */ spin_lock(&tfile->f_lock); list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links); - epi->on_list = 1; spin_unlock(&tfile->f_lock); /* @@ -1347,8 +1339,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, error_remove_epi: spin_lock(&tfile->f_lock); - if (epi->on_list) - list_del_rcu(&epi->fllink); + list_del_rcu(&epi->fllink); spin_unlock(&tfile->f_lock); rb_erase(&epi->rbn, &ep->rbr); -- 2.39.5