epoll: avoid double-inserts in case of EFAULT
In commit f337b9c583
("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>
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parent
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@ -930,8 +930,15 @@ errxit:
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* inside the main ready-list here.
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* inside the main ready-list here.
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*/
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*/
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for (nepi = ep->ovflist; (epi = nepi) != NULL;
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for (nepi = ep->ovflist; (epi = nepi) != NULL;
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nepi = epi->next, epi->next = EP_UNACTIVE_PTR)
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nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
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/*
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* If the above loop quit with errors, the epoll item might still
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* be linked to "txlist", and the list_splice() done below will
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* take care of those cases.
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*/
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if (!ep_is_linked(&epi->rdllink))
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list_add_tail(&epi->rdllink, &ep->rdllist);
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list_add_tail(&epi->rdllink, &ep->rdllist);
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}
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/*
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/*
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* We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
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* We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
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* releasing the lock, events will be queued in the normal way inside
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* releasing the lock, events will be queued in the normal way inside
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