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Commit 06a77b07 authored by WANG Cong's avatar WANG Cong Committed by David S. Miller
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af_unix: conditionally use freezable blocking calls in read 



Commit 2b15af6f ("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 2b514574
("net: af_unix: implement splice for stream af_unix sockets") breaks
the strong requirement for a freezable sleep, according to
commit 0f9548ca:

    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.

Fixes: 2b514574 ("net: af_unix: implement splice for stream af_unix sockets")
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Colin Cross <ccross@android.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0e2d1af3

net/unix/af_unix.c

+11 −6
Original line number Diff line number Diff line
@@ -2199,7 +2199,8 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, 
 *	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);
@@ -2220,7 +2221,10 @@ static long unix_stream_data_wait(struct sock *sk, long timeo, 


		sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);

		unix_state_unlock(sk);

		if (freezable)

			timeo = freezable_schedule_timeout(timeo);

		else

			timeo = schedule_timeout(timeo);

		unix_state_lock(sk);



		if (sock_flag(sk, SOCK_DEAD))
@@ -2250,7 +2254,8 @@ 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;
@@ -2330,7 +2335,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state) 
			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);
@@ -2472,7 +2477,7 @@ static int unix_stream_recvmsg(struct socket *sock, struct msghdr *msg, 
		.flags = flags

	};



	return unix_stream_read_generic(&state);

	return unix_stream_read_generic(&state, true);

}



static int unix_stream_splice_actor(struct sk_buff *skb,
@@ -2503,7 +2508,7 @@ static ssize_t unix_stream_splice_read(struct socket *sock, loff_t *ppos, 
	    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)