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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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