Messages in this thread | | | Date | Mon, 13 Feb 2023 18:43:59 +0900 | Subject | Re: [PATCH v3] locking/lockdep: add debug_show_all_lock_holders() | From | Tetsuo Handa <> |
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Ingo or Peter, are you there?
Linus is expecting that this patch (if acceptable) is sent from the locking people.
https://lkml.kernel.org/r/CAHk-=wjbu9USn=hVWQ9v9t1H+8R6qXj8REkm36==w10zM0cM6g@mail.gmail.com
On 2023/02/02 22:59, 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. > > debug_show_all_lock_holders() skips current thread if the caller is > holding no lock, for reporting RCU lock taken inside that function is > generally useless. > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > --- > Changes in v3: > Unshare debug_show_all_lock_holders() and debug_show_all_locks(), > suggested by Ingo Molnar <mingo@kernel.org>. > > Changes in v2: > Share debug_show_all_lock_holders() and debug_show_all_locks(), > suggested by Waiman Long <longman@redhat.com>. > > include/linux/debug_locks.h | 5 +++++ > kernel/hung_task.c | 2 +- > kernel/locking/lockdep.c | 28 ++++++++++++++++++++++++++++ > 3 files changed, 34 insertions(+), 1 deletion(-) >
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