Patch "af_unix: Revert 'lock_interruptible' in stream receive code" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

af_unix: Revert 'lock_interruptible' in stream receive code

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
af_unix-revert-lock_interruptible-in-stream-receive-code.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Rainer Weikusat <[email protected]>
Date: Wed, 16 Dec 2015 20:09:25 +0000
Subject: af_unix: Revert 'lock_interruptible' in stream receive code

From: Rainer Weikusat <[email protected]>

[ Upstream commit 3822b5c2fc62e3de8a0f33806ff279fb7df92432 ]

With b3ca9b02b00704053a38bfe4c31dbbb9c13595d0, 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.

---
 net/unix/af_unix.c |   13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

@@ -2255,14 +2255,7 @@ static int unix_stream_read_generic(stru
 	/* 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);

@@ -2306,12 +2299,12 @@ 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/af_unix-revert-lock_interruptible-in-stream-receive-code.patch