Patch "usblp: do not set TASK_INTERRUPTIBLE before lock" has been added to the 4.2-stable tree

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

usblp: do not set TASK_INTERRUPTIBLE before lock

to the 4.2-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:
usblp-do-not-set-task_interruptible-before-lock.patch
and it can be found in the queue-4.2 subdirectory.

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

From: Jiri Slaby <[email protected]>
Date: Mon, 2 Nov 2015 10:27:00 +0100
Subject: usblp: do not set TASK_INTERRUPTIBLE before lock

From: Jiri Slaby <[email protected]>

commit 19cd80a214821f4b558560ebd76bfb2c38b4f3d8 upstream.

It is not permitted to set task state before lock. usblp_wwait sets the state to TASK_INTERRUPTIBLE and calls mutex_lock_interruptible. Upon return from that function, the state will be TASK_RUNNING again.

This is clearly a bug and a warning is generated with LOCKDEP too:

WARNING: CPU: 1 PID: 5109 at kernel/sched/core.c:7404 __might_sleep+0x7d/0x90()
do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffffa0c588d0>] usblp_wwait+0xa0/0x310 [usblp]
Modules linked in: ...
CPU: 1 PID: 5109 Comm: captmon Tainted: G        W       4.2.5-0.gef2823b-default #1
Hardware name: LENOVO 23252SG/23252SG, BIOS G2ET33WW (1.13 ) 07/24/2012
 ffffffff81a4edce ffff880236ec7ba8 ffffffff81716651 0000000000000000
 ffff880236ec7bf8 ffff880236ec7be8 ffffffff8106e146 0000000000000282
 ffffffff81a50119 000000000000028b 0000000000000000 ffff8802dab7c508
Call Trace:
...
 [<ffffffff8106e1c6>] warn_slowpath_fmt+0x46/0x50
 [<ffffffff8109a8bd>] __might_sleep+0x7d/0x90
 [<ffffffff8171b20f>] mutex_lock_interruptible_nested+0x2f/0x4b0
 [<ffffffffa0c588fc>] usblp_wwait+0xcc/0x310 [usblp]
 [<ffffffffa0c58bb2>] usblp_write+0x72/0x350 [usblp]
 [<ffffffff8121ed98>] __vfs_write+0x28/0xf0

...

Commit 7f477358e2384c54b190cc3b6ce28277050a041b (usblp: Implement the ENOSPC convention) moved the set prior locking. So move it back after the lock.

---
 drivers/usb/class/usblp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -873,11 +873,11 @@ static int usblp_wwait(struct usblp *usb
 
 	add_wait_queue(&usblp->wwait, &waita);
 	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
 		if (mutex_lock_interruptible(&usblp->mut)) {
 			rc = -EINTR;
 			break;
 		}
+		set_current_state(TASK_INTERRUPTIBLE);
 		rc = usblp_wtest(usblp, nonblock);
 		mutex_unlock(&usblp->mut);
 		if (rc <= 0)

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

queue-4.2/usblp-do-not-set-task_interruptible-before-lock.patch