[PATCH 4.8 07/45] af_unix: conditionally use freezable blocking calls in read

From: Greg Kroah-Hartman
Date: Fri Dec 09 2016 - 11:24:00 EST

4.8-stable review patch. If anyone has any objections, please let me know.


From: WANG Cong <xiyou.wangcong@xxxxxxxxx>

[ 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

Fixes: 2b514574f7e8 ("net: af_unix: implement splice for stream af_unix sockets")
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/unix/af_unix.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2199,7 +2199,8 @@ 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;
@@ -2220,7 +2221,10 @@ static long unix_stream_data_wait(struct

sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
- timeo = freezable_schedule_timeout(timeo);
+ if (freezable)
+ timeo = freezable_schedule_timeout(timeo);
+ else
+ timeo = schedule_timeout(timeo);

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 @@ again:

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 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,
@@ -2518,7 +2523,7 @@ static ssize_t unix_stream_splice_read(s
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)