Commit 3822b5c2 authored Dec 16, 2015 by Rainer Weikusat Committed by David S. Miller Dec 17, 2015

af_unix: Revert 'lock_interruptible' in stream receive code

With b3ca9b02, the AF_UNIX SOCK_STREAM
receive code was changed from using mutex_lock(&u->readlock) to
mutex_lock_interruptible(&u->readlock) to prevent signals from being
delayed for an indefinite time if a thread sleeping on the mutex
happened to be selected for handling the signal. But this was never a
problem with the stream receive code (as opposed to its datagram
counterpart) as that never went to sleep waiting for new messages with the
mutex held and thus, wouldn't cause secondary readers to block on the
mutex waiting for the sleeping primary reader. As the interruptible
locking makes the code more complicated in exchange for no benefit,
change it back to using mutex_lock.

Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 3036facb

net/unix/af_unix.c

+3 −10

Original line number	Diff line number	Diff line
		@@ -2256,14 +2256,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
		/* Lock the socket to prevent queue disordering
		* while sleeps in memcpy_tomsg
		*/
		err = mutex_lock_interruptible(&u->readlock);
		if (unlikely(err)) {
		/* recvmsg() in non blocking mode is supposed to return -EAGAIN
		* sk_rcvtimeo is not honored by mutex_lock_interruptible()
		*/
		err = noblock ? -EAGAIN : -ERESTARTSYS;
		goto out;
		}
		mutex_lock(&u->readlock);

		if (flags & MSG_PEEK)
		skip = sk_peek_offset(sk, flags);
		@@ -2307,12 +2300,12 @@ again:
		timeo = unix_stream_data_wait(sk, timeo, last,
		last_len);

		if (signal_pending(current) \|\|
		mutex_lock_interruptible(&u->readlock)) {
		if (signal_pending(current)) {
		err = sock_intr_errno(timeo);
		goto out;
		}

		mutex_lock(&u->readlock);
		continue;
		unlock:
		unix_state_unlock(sk);

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