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net: add POLLPRI to sock_def_readable()

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Leonardo Chiquitto found poll() could block forever on tcp sockets and
Urgent data was received, if the event flag only contains POLLPRI.

He did a bisection and found commit 4938d7e0233 (poll: avoid extra
wakeups in select/poll) was the source of the problem.

Problem is TCP sockets use standard sock_def_readable() function for
their sk_data_ready() handler, and sock_def_readable() doesnt signal
POLLPRI.

Only TCP is affected by the problem. Adding POLLPRI to the list of flags
might trigger unnecessary schedules, but URGENT handling is such a
seldom used feature this seems a good compromise.

Thanks a lot to Leonardo for providing the bisection result and a test
program as well.

Reference : http://www.spinics.net/lists/netdev/msg151793.html

Reported-and-bisected-by: Leonardo Chiquitto <leonardo.lists@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2011-01-06 10:54:29 -08:00 committed by David S. Miller
parent 3610cda53f
commit 2c6607c611
1 changed files with 1 additions and 1 deletions
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2
net/core/sock.c
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@ -1908,7 +1908,7 @@ static void sock_def_readable(struct sock *sk, int len)
rcu_read_lock(); rcu_read_lock();
wq = rcu_dereference(sk->sk_wq); wq = rcu_dereference(sk->sk_wq);
if (wq_has_sleeper(wq)) if (wq_has_sleeper(wq))
wake_up_interruptible_sync_poll(&wq->wait, POLLIN | wake_up_interruptible_sync_poll(&wq->wait, POLLIN | POLLPRI |
POLLRDNORM | POLLRDBAND); POLLRDNORM | POLLRDBAND);
sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
rcu_read_unlock(); rcu_read_unlock();