[PATCHSET] workqueue, writeback: better worker information in task dumps

[Tejun Heo <tj@kernel.org>]

Hello,

One of the problems that arise when converting dedicated custom
threadpool to workqueue is that the shared worker pool used by
workqueue anonimizes each worker making it more difficult to identify
what the worker was doing on which target from the output of sysrq-t
or debug dump from oops, BUG() and friends.

For example, after writeback is converted to use workqueue instead of
priviate thread pool, there's no easy to tell which backing device a
writeback work item was working on at the time of task dump, which,
according to our writeback brethren, is important in tracking down
issues with a lot of mounted file systems on a lot of different
devices.

This patchset implements a way for a work function to mark its
execution instance so that task dump of the worker task includes
information to indicate what the work item was doing.

An example WARN dump would look like the following.

 WARNING: at /work/os/work/fs/fs-writeback.c:1015 bdi_writeback_workfn+0x2b4/0x3c0()
 Modules linked in:
 Pid: 28, comm: kworker/u18:0 Not tainted 3.9.0-rc1-work+ #24 empty empty/S3992
 Workqueue: writeback bdi_writeback_workfn (flush-8:16)
  ffffffff820a3a98 ffff88015b927cb8 ffffffff81c61855 ffff88015b927cf8
  ffffffff8108f500 0000000000000000 ffff88007a171948 ffff88007a1716b0
  ffff88015b49df00 ffff88015b8d3940 0000000000000000 ffff88015b927d08
 Call Trace:
  [<ffffffff81c61855>] dump_stack+0x19/0x1b
  [<ffffffff8108f500>] warn_slowpath_common+0x70/0xa0
  ...

This patchset contains the following three patches.

 0001-kthread-implement-probe_kthread_data.patch
 0002-workqueue-include-workqueue-info-when-printing-debug.patch
 0003-writeback-set-worker-desc-to-identify-writeback-work.patch

0001 adds a speculative accessor for kthread_data.

0002 implements worker description.

0003 updates writeback to set its flusher name as worker description.

This patchset is on top of

  [1] workqueue: NUMA affinity for unbound workqueues
+ [2] writeback: convert writeback to unbound workqueue
+ [3] arch: unify task dump debug info

and available in the following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git review-better-dbg

Due to the dependencies, routing this set would be a bit complicated.
I think it would be best to first pull wq/for-3.10 to block tree and
apply workqueue conversion patchset.  The patches in this series then
can go through -mm on top of all three pieces - workqueue, block and
archs.

diffstat follows.  Thanks.

 fs/fs-writeback.c           |    1 
 include/linux/kthread.h     |    1 
 include/linux/workqueue.h   |    5 ++
 kernel/kthread.c            |   19 ++++++++++
 kernel/sched/core.c         |    1 
 kernel/workqueue.c          |   79 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/workqueue_internal.h |   12 ++++++
 lib/dump_stack.c            |    2 +
 8 files changed, 119 insertions(+), 1 deletion(-)

--
tejun

[1] http://thread.gmane.org/gmane.linux.kernel/1465626
[2] http://thread.gmane.org/gmane.linux.kernel/1453006
[3] https://lkml.org/lkml/2013/3/29/354