Messages in this thread | | | Date | Tue, 4 Oct 2022 14:09:39 -0400 | Subject | Re: [PATCH v2] locking/lockdep: add debug_show_all_lock_holders() | From | Waiman Long <> |
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On 10/3/22 18:18, Tetsuo Handa wrote: > Can this patch go to linux.git ?
It is now up to Peter or Ingo to take it to tip.
Cheers, Longman
> > On 2022/09/17 3:41, Waiman Long wrote: >> On 9/16/22 11:57, Tetsuo Handa wrote: >>> Currently, check_hung_uninterruptible_tasks() reports details of locks >>> held in the system. Also, lockdep_print_held_locks() does not report >>> details of locks held by a thread if that thread is in TASK_RUNNING state. >>> Several years of experience of debugging without vmcore tells me that >>> these limitations have been a barrier for understanding what went wrong >>> in syzbot's "INFO: task hung in" reports. >>> >>> I initially thought that the cause of "INFO: task hung in" reports is >>> due to over-stressing. But I understood that over-stressing is unlikely. >>> I now consider that there likely is a deadlock/livelock bug where lockdep >>> cannot report as a deadlock when "INFO: task hung in" is reported. >>> >>> A typical case is that thread-1 is waiting for something to happen (e.g. >>> wait_event_*()) with a lock held. When thread-2 tries to hold that lock >>> using e.g. mutex_lock(), check_hung_uninterruptible_tasks() reports that >>> thread-2 is hung and thread-1 is holding a lock which thread-2 is trying >>> to hold. But currently check_hung_uninterruptible_tasks() cannot report >>> the exact location of thread-1 which gives us an important hint for >>> understanding why thread-1 is holding that lock for so long period. >>> >>> When check_hung_uninterruptible_tasks() reports a thread waiting for a >>> lock, it is important to report backtrace of threads which already held >>> that lock. Therefore, allow check_hung_uninterruptible_tasks() to report >>> the exact location of threads which is holding any lock. >>> >>> To deduplicate code, share debug_show_all_{locks,lock_holders}() using >>> a flag. As a side effect of sharing, __debug_show_all_locks() skips >>> current thread if the caller is holding no lock, for reporting RCU lock >>> taken inside __debug_show_all_locks() is generally useless. >>> >>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> >> Acked-by: Waiman Long <longman@redhat.com>
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