netdev - [Patch net] af_unix: revert "af_unix: use freezable blocking calls in read"

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Date:   Thu, 17 Nov 2016 14:09:24 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     dvyukov@...gle.com, Cong Wang <xiyou.wangcong@...il.com>,
        Tejun Heo <tj@...nel.org>, Colin Cross <ccross@...roid.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [Patch net] af_unix: revert "af_unix: use freezable blocking calls in read"

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 just revert commit 2b15af6f95.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Colin Cross <ccross@...roid.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/unix/af_unix.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 5d1c14a..6f37f9e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -116,7 +116,6 @@
 #include <linux/mount.h>
 #include <net/checksum.h>
 #include <linux/security.h>
-#include <linux/freezer.h>
 
 struct hlist_head unix_socket_table[2 * UNIX_HASH_SIZE];
 EXPORT_SYMBOL_GPL(unix_socket_table);
@@ -2220,7 +2219,7 @@ static long unix_stream_data_wait(struct sock *sk, long timeo,
 
 		sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
 		unix_state_unlock(sk);
-		timeo = freezable_schedule_timeout(timeo);
+		timeo = schedule_timeout(timeo);
 		unix_state_lock(sk);
 
 		if (sock_flag(sk, SOCK_DEAD))
-- 
2.1.0