Messages in this thread | | | Date | Tue, 4 Oct 2022 07:18:23 +0900 | Subject | Re: [PATCH v2] locking/lockdep: add debug_show_all_lock_holders() | From | Tetsuo Handa <> |
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Can this patch go to linux.git ?
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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