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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.