Messages in this thread | | | Date | Mon, 14 Nov 2022 19:05:51 +0900 | Subject | Re: [PATCH v2] locking/lockdep: add debug_show_all_lock_holders() | From | Tetsuo Handa <> |
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Peter or Ingo, can you take this patch?
On 2022/10/05 3:09, Waiman Long wrote: > 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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