Patch "af_unix: conditionally use freezable blocking calls in read" has been added to the 4.4-stable tree

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

af_unix: conditionally use freezable blocking calls in read

to the 4.4-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-conditionally-use-freezable-blocking-calls-in-read.patch
and it can be found in the queue-4.4 subdirectory.

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

From: WANG Cong <[email protected]>
Date: Thu, 17 Nov 2016 15:55:26 -0800
Subject: af_unix: conditionally use freezable blocking calls in read

From: WANG Cong <[email protected]>

[ Upstream commit 06a77b07e3b44aea2b3c0e64de420ea2cfdcbaa9 ]

Commit 2b15af6f95 ("af_unix: use freezable blocking calls in read") converts schedule_timeout() to its freezable version, it was probably correct at that time, but later, commit 2b514574f7e8 ("net: af_unix: implement splice for stream af_unix sockets") breaks the strong requirement for a freezable sleep, according to commit 0f9548ca1091:

We shouldn't try_to_freeze if locks are held. Holding a lock can cause a deadlock if the lock is later acquired in the suspend or hibernate path (e.g. by dpm). Holding a lock can also cause a deadlock in the case of cgroup_freezer if a lock is held inside a frozen cgroup that is later acquired by a process outside that group.

The pipe_lock is still held at that point.

So use freezable version only for the recvmsg call path, avoid impact for Android.

---
 net/unix/af_unix.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

@@ -2194,7 +2194,8 @@ out:
  *	Sleep until more data has arrived. But check for races..
  */
 static long unix_stream_data_wait(struct sock *sk, long timeo,
-				  struct sk_buff *last, unsigned int last_len)
+				  struct sk_buff *last, unsigned int last_len,
+				  bool freezable)
 {
 	struct sk_buff *tail;
 	DEFINE_WAIT(wait);

@@ -2215,7 +2216,10 @@ static long unix_stream_data_wait(struct
 
 		sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
 		unix_state_unlock(sk);
-		timeo = freezable_schedule_timeout(timeo);
+		if (freezable)
+			timeo = freezable_schedule_timeout(timeo);
+		else
+			timeo = schedule_timeout(timeo);
 		unix_state_lock(sk);
 
 		if (sock_flag(sk, SOCK_DEAD))

@@ -2245,7 +2249,8 @@ struct unix_stream_read_state {
 	unsigned int splice_flags;
 };
 
-static int unix_stream_read_generic(struct unix_stream_read_state *state)
+static int unix_stream_read_generic(struct unix_stream_read_state *state,
+				    bool freezable)
 {
 	struct scm_cookie scm;
 	struct socket *sock = state->socket;

@@ -2324,7 +2329,7 @@ again:
 			mutex_unlock(&u->iolock);
 
 			timeo = unix_stream_data_wait(sk, timeo, last,
-						      last_len);
+						      last_len, freezable);
 
 			if (signal_pending(current)) {
 				err = sock_intr_errno(timeo);

@@ -2466,7 +2471,7 @@ static int unix_stream_recvmsg(struct so
 		.flags = flags
 	};
 
-	return unix_stream_read_generic(&state);
+	return unix_stream_read_generic(&state, true);
 }
 
 static ssize_t skb_unix_socket_splice(struct sock *sk,

@@ -2512,7 +2517,7 @@ static ssize_t unix_stream_splice_read(s
 	    flags & SPLICE_F_NONBLOCK)
 		state.flags = MSG_DONTWAIT;
 
-	return unix_stream_read_generic(&state);
+	return unix_stream_read_generic(&state, false);
 }
 
 static int unix_shutdown(struct socket *sock, int mode)

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

queue-4.4/net-sched-respect-rcu-grace-period-on-cls-destruction.patch queue-4.4/af_unix-conditionally-use-freezable-blocking-calls-in-read.patch queue-4.4/netlink-call-cb-done-from-a-worker-thread.patch queue-4.4/net-check-dead-netns-for-peernet2id_alloc.patch