Patch "ceph: fix scheduler warning due to nested blocking" has been added to the 4.9-stable tree

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

ceph: fix scheduler warning due to nested blocking

to the 4.9-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:
ceph-fix-scheduler-warning-due-to-nested-blocking.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Nikolay Borisov <[email protected]>
Date: Tue, 11 Oct 2016 12:04:09 +0300
Subject: ceph: fix scheduler warning due to nested blocking

From: Nikolay Borisov <[email protected]>

commit 5c341ee32881c554727ec14b71ec3e8832f01989 upstream.

try_get_cap_refs can be used as a condition in a wait_event* calls. This is all fine until it has to call __ceph_do_pending_vmtruncate, which in turn acquires the i_truncate_mutex. This leads to a situation in which a task's state is !TASK_RUNNING and at the same time it's trying to acquire a sleeping primitive. In essence a nested sleeping primitives are being used. This causes the following warning:

WARNING: CPU: 22 PID: 11064 at kernel/sched/core.c:7631 __might_sleep+0x9f/0xb0()
do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff8109447d>] prepare_to_wait_event+0x5d/0x110
 ipmi_msghandler tcp_scalable ib_qib dca ib_mad ib_core ib_addr ipv6
CPU: 22 PID: 11064 Comm: fs_checker.pl Tainted: G           O    4.4.20-clouder2 #6
Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1a 10/16/2015
 0000000000000000 ffff8838b416fa88 ffffffff812f4409 ffff8838b416fad0
 ffffffff81a034f2 ffff8838b416fac0 ffffffff81052b46 ffffffff81a0432c
 0000000000000061 0000000000000000 0000000000000000 ffff88167bda54a0
Call Trace:
 [<ffffffff812f4409>] dump_stack+0x67/0x9e
 [<ffffffff81052b46>] warn_slowpath_common+0x86/0xc0
 [<ffffffff81052bcc>] warn_slowpath_fmt+0x4c/0x50
 [<ffffffff8109447d>] ? prepare_to_wait_event+0x5d/0x110
 [<ffffffff8109447d>] ? prepare_to_wait_event+0x5d/0x110
 [<ffffffff8107767f>] __might_sleep+0x9f/0xb0
 [<ffffffff81612d30>] mutex_lock+0x20/0x40
 [<ffffffffa04eea14>] __ceph_do_pending_vmtruncate+0x44/0x1a0 [ceph]
 [<ffffffffa04fa692>] try_get_cap_refs+0xa2/0x320 [ceph]
 [<ffffffffa04fd6f5>] ceph_get_caps+0x255/0x2b0 [ceph]
 [<ffffffff81094370>] ? wait_woken+0xb0/0xb0
 [<ffffffffa04f2c11>] ceph_write_iter+0x2b1/0xde0 [ceph]
 [<ffffffff81613f22>] ? schedule_timeout+0x202/0x260
 [<ffffffff8117f01a>] ? kmem_cache_free+0x1ea/0x200
 [<ffffffff811b46ce>] ? iput+0x9e/0x230
 [<ffffffff81077632>] ? __might_sleep+0x52/0xb0
 [<ffffffff81156147>] ? __might_fault+0x37/0x40
 [<ffffffff8119e123>] ? cp_new_stat+0x153/0x170
 [<ffffffff81198cfa>] __vfs_write+0xaa/0xe0
 [<ffffffff81199369>] vfs_write+0xa9/0x190
 [<ffffffff811b6d01>] ? set_close_on_exec+0x31/0x70
 [<ffffffff8119a056>] SyS_write+0x46/0xa0

This happens since wait_event_interruptible can interfere with the mutex locking code, since they both fiddle with the task state.

Fix the issue by using the newly-added nested blocking infrastructure in 61ada528dea0 ("sched/wait: Provide infrastructure to deal with nested blocking")

---
 fs/ceph/caps.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

@@ -2507,9 +2507,15 @@ int ceph_get_caps(struct ceph_inode_info
 			if (err < 0)
 				ret = err;
 		} else {
-			ret = wait_event_interruptible(ci->i_cap_wq,
-					try_get_cap_refs(ci, need, want, endoff,
-							 true, &_got, &err));
+			DEFINE_WAIT_FUNC(wait, woken_wake_function);
+			add_wait_queue(&ci->i_cap_wq, &wait);
+
+			while (!try_get_cap_refs(ci, need, want, endoff,
+						 true, &_got, &err))
+				wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
+
+			remove_wait_queue(&ci->i_cap_wq, &wait);
+
 			if (err == -EAGAIN)
 				continue;
 			if (err < 0)

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

queue-4.9/ceph-fix-scheduler-warning-due-to-nested-blocking.patch