From 9ce209d64d820a6d5ed6b952e2c0f917faad6031 Mon Sep 17 00:00:00 2001 From: Davide Libenzi Date: Fri, 17 Oct 2008 16:17:40 -0700 Subject: epoll: avoid double-inserts in case of EFAULT In commit f337b9c58332bdecde965b436e47ea4c94d30da0 ("epoll: drop unnecessary test") Thomas found that there is an unnecessary (always true) test in ep_send_events(). The callback never inserts into ->rdllink while the send loop is performed, and also does the ~EP_PRIVATE_BITS test. Given we're holding the mutex during this time, the conditions tested inside the loop are always true. HOWEVER. The test "!ep_is_linked(&epi->rdllink)" wasn't there because we insert into ->rdllink, but because the send-events loop might terminate before the whole list is scanned (-EFAULT). In such cases, when the loop terminates early, and when a (leftover) file received an event while we're performing the lockless loop, we need such test to avoid to double insert the epoll items. The list_splice() done a few steps below, will correctly re-insert the ones that were left on "txlist". This should fix the kenrel.org bugzilla entry 11831. Signed-off-by: Davide Libenzi Signed-off-by: Linus Torvalds --- fs/eventpoll.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 99368bda026..aec5c13f634 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -930,8 +930,15 @@ errxit: * inside the main ready-list here. */ for (nepi = ep->ovflist; (epi = nepi) != NULL; - nepi = epi->next, epi->next = EP_UNACTIVE_PTR) - list_add_tail(&epi->rdllink, &ep->rdllist); + nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { + /* + * If the above loop quit with errors, the epoll item might still + * be linked to "txlist", and the list_splice() done below will + * take care of those cases. + */ + if (!ep_is_linked(&epi->rdllink)) + list_add_tail(&epi->rdllink, &ep->rdllist); + } /* * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after * releasing the lock, events will be queued in the normal way inside -- cgit v1.2.3