Messages in this thread | | | Date | Sun, 22 Dec 2013 16:09:18 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] skip increamenting nr for TASK_UNINTERRUPTIBLE |
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Vaibhav,
again, I think that everything was explained by Linus, let me add some details.
> > In coredump case, where thread_1 faults while thread_2 is in > > TASK_UNINTERRUPTIBLE state, it cannot handle the SIGKILL. > > Thus the process hangs on event. > > The coredump routine freezes until the thread state is > > uninterruptible.
Yes. But why we should even try to "fix" coredump in this case?
> > Solution: Continue for coredump, without waiting for uninterruptible > > thread,
This can't work, please see below.
> > as it will get killed as soon as it returns from > > uninterruptible state.
Not necessarily. It can play with ->mm before it notices the pending SIGKILL. And, if nothing else, the coredumping paths do not even take mmap_sem because we assume that the dumper is the only user.
But even if this doesn't happen,
> > Therefore do not increament thread count for threads with > > TASK_UNINTERRUPTIBLE.
This is very wrong too. This means that we can start the coredump before the _accounted_ thread exits (because a skipped thread can exit first and decrement the counter). This also means that coredump_finish() can race with the unaccounted threads.
> > sigaddset(&t->pending.signal, SIGKILL); > > signal_wake_up(t, 1); > > - nr++; > > + if(!(t->state & TASK_UNINTERRUPTIBLE)) > > + nr++;
Again, we can't simply check t->state & TASK_UNINTERRUPTIBLE. This can be false positive or it can sleep in TASK_UNINTERRUPTIBLE right after the check. And even "& TASK_UNINTERRUPTIBLE" is wrong, please look at TASK_KILLABLE.
Oleg.
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