• Tejun Heo's avatar
    kthread: implement probe_kthread_data() · cd42d559
    Tejun Heo authored
    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 fs/fs-writeback.c:1015 bdi_writeback_workfn+0x2b4/0x3c0()
     Modules linked in:
     CPU: 0 Pid: 28 Comm: kworker/u18:0 Not tainted 3.9.0-rc1-work+ #24
     Hardware name: empty empty/S3992, BIOS 080011  10/26/2007
     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 patch:
    
    Implement probe_kthread_data() which returns kthread_data if accessible.
    The function is equivalent to kthread_data() except that the specified
    @task may not be a kthread or its vfork_done is already cleared rendering
    struct kthread inaccessible.  In the former case, probe_kthread_data() may
    return any value.  In the latter, NULL.
    
    This will be used to safely print debug information without affecting
    synchronization in the normal paths.  Workqueue debug info printing on
    dump_stack() and friends will make use of it.
    Signed-off-by: 's avatarTejun Heo <tj@kernel.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Acked-by: 's avatarJan Kara <jack@suse.cz>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    cd42d559
kthread.c 17.6 KB