diff options
| author | Jason Baron <jbaron@akamai.com> | 2013-11-05 16:56:59 +1100 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2013-11-05 16:56:59 +1100 |
| commit | e8895a983c866ec3261f9881e27a5eeb151cb6b4 (patch) | |
| tree | 6855d96cbf21888e5f75beb0fdbef91df6dae516 /fs | |
| parent | 1d623672204845ff4e916ccbf5da2e826d5e8c35 (diff) | |
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 <jbaron@akamai.com>
Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Nathan Zimmer <nzimmer@sgi.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Nelson Elhage <nelhage@nelhage.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/eventpoll.c | 13 |
1 files 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); |