Messages in this thread Patch in this message | | | Date | Mon, 18 Feb 2013 15:55:44 -0800 | Subject | Re: [PATCH 5/5] coredump: ignore non-fatal signals when core dumping to a pipe | From | Mandeep Singh Baines <> |
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On Sat, Feb 16, 2013 at 11:46 AM, Oleg Nesterov <oleg@redhat.com> wrote: > On 02/16, Oleg Nesterov wrote: >> >> On 02/16, Mandeep Singh Baines wrote: >> > >> > +static int sigkill_pending(struct task_struct *tsk) >> > +{ >> > + return signal_pending(tsk) && >> > + (sigismember(&tsk->pending.signal, SIGKILL) || >> > + sigismember(&tsk->signal->shared_pending.signal, SIGKILL)); >> > +} >> >> Why? __fatal_signal_pending() is enough, you do not need to check >> ->shared_pending. And once again, ignoring the freezer problems I >> do not think we need this check at all. >>
The problem is that the kill signal remains in shared pending since it'll never get dequeued.
localhost ~ # kill -KILL $! localhost ~ # cat /proc/$!/status | grep -A4 SigPnd SigPnd: 0000000000000000 ShdPnd: 0000000000000100 SigBlk: 0000000000000000 SigIgn: 0000000000000000 SigCgt: 0000000000000000
Normally a fatal signal will get propagated to the whole group but that doesn't happen here because GROUP_EXIT is set:
/* * Found a killable thread. If the signal will be fatal, * then start taking the whole group down immediately. */ if (sig_fatal(p, sig) && !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) && !sigismember(&t->real_blocked, sig) && (sig == SIGKILL || !t->ptrace)) { /* * This signal will be fatal to the whole group. */
GROUP_EXIT is set in do_coredump->coredump_wait->zap_threads->zap_process.
What if complete_signal was changed to propagate KILL even if SIGNAL_GROUP_EXIT is set?
Regards, Mandeep
>> IOW. Yes, we will probably need to do this change but only to be >> freezer-friendly. > > And, forgot to mention, this logic is not right in the multi- > threaded case. I mean, you can't assume that 'kill -9 dumpingtask" > will wake the coredumping thread up. So this sigkill_pending() or > __fatal_signal_pending() check can only work in the single-threaded > case. > >> --- x/fs/coredump.c >> +++ x/fs/coredump.c >> @@ -416,17 +416,17 @@ static void wait_for_dump_helpers(struct >> pipe_lock(pipe); >> pipe->readers++; >> pipe->writers--; >> + // TODO: wake_up_interruptible_sync_poll ? >> + wake_up_interruptible_sync(&pipe->wait); >> + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); >> + pipe_unlock(pipe); >> >> - while ((pipe->readers > 1) && (!signal_pending(current))) { >> - wake_up_interruptible_sync(&pipe->wait); >> - kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); >> - pipe_wait(pipe); >> - } >> + wait_event_freezekillable(&pipe->wait, pipe->readers == 1); > > I tried to check (but didn't even try to test). I think this should > work. Assuming that we teach SIGKILL to actually kill the dumper, but > we need this in any case. > > But. Then we need to change pipe_release() to use wake_up_sync_poll() > (which we do not have). Probably we can do this... but otoh if we protect > the dumping thread from the non-fatal signals (and again, we need this > anyway ;) then we can simply do wait_event_freezable(). > > Damn. I need to think more. > > Oleg. >
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