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Subject[PATCH 4.4 26/60] dm kcopyd: avoid softlockup in run_complete_job
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: John Pittman <jpittman@redhat.com>

[ Upstream commit 784c9a29e99eb40b842c29ecf1cc3a79e00fb629 ]

It was reported that softlockups occur when using dm-snapshot ontop of
slow (rbd) storage. E.g.:

[ 4047.990647] watchdog: BUG: soft lockup - CPU#10 stuck for 22s! [kworker/10:23:26177]
...
[ 4048.034151] Workqueue: kcopyd do_work [dm_mod]
[ 4048.034156] RIP: 0010:copy_callback+0x41/0x160 [dm_snapshot]
...
[ 4048.034190] Call Trace:
[ 4048.034196] ? __chunk_is_tracked+0x70/0x70 [dm_snapshot]
[ 4048.034200] run_complete_job+0x5f/0xb0 [dm_mod]
[ 4048.034205] process_jobs+0x91/0x220 [dm_mod]
[ 4048.034210] ? kcopyd_put_pages+0x40/0x40 [dm_mod]
[ 4048.034214] do_work+0x46/0xa0 [dm_mod]
[ 4048.034219] process_one_work+0x171/0x370
[ 4048.034221] worker_thread+0x1fc/0x3f0
[ 4048.034224] kthread+0xf8/0x130
[ 4048.034226] ? max_active_store+0x80/0x80
[ 4048.034227] ? kthread_bind+0x10/0x10
[ 4048.034231] ret_from_fork+0x35/0x40
[ 4048.034233] Kernel panic - not syncing: softlockup: hung tasks

Fix this by calling cond_resched() after run_complete_job()'s callout to
the dm_kcopyd_notify_fn (which is dm-snap.c:copy_callback in the above
trace).

Signed-off-by: John Pittman <jpittman@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-kcopyd.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -454,6 +454,8 @@ static int run_complete_job(struct kcopy
if (atomic_dec_and_test(&kc->nr_jobs))
wake_up(&kc->destroyq);

+ cond_resched();
+
return 0;
}


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