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author | Davide Libenzi <davidel@xmailserver.org> | 2008-10-17 23:17:40 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-10-26 19:09:49 (GMT) |
commit | 9ce209d64d820a6d5ed6b952e2c0f917faad6031 (patch) | |
tree | 817c5bd01e6666c8269d29d3d8292b5e75ea7fb3 /fs | |
parent | 4d36a9e65d4966b433b2f3424d9457468bc80e00 (diff) | |
download | linux-fsl-qoriq-9ce209d64d820a6d5ed6b952e2c0f917faad6031.tar.xz |
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 <davidel@xmailserver.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/eventpoll.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 99368bd..aec5c13f 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 |