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__group_complete_signal(): fix coredump with group stop race 

When __group_complete_signal() sees sig_kernel_coredump() signal, it starts
the group stop, but sets ->group_exit_task = t in a hope that "t" will
actually dequeue this signal and invoke do_coredump().  However, by the
time "t" enters get_signal_to_deliver() it is possible that the signal was
blocked/ignored or we have another pending !SIG_KERNEL_COREDUMP_MASK signal
which will be dequeued first.  This means the task could be stopped but not
killed.

Remove this code from __group_complete_signal().  Note also this patch
removes the bogus signal_wake_up(t, 1).  This thread can't be
STOPPED/TRACED, note the corresponding check in wants_signal().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Robin Holt <holt@sgi.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-02-04 22:27:23 -08:00 committed by Linus Torvalds
parent bdff746a39
commit 198466b41d
1 changed files with 0 additions and 30 deletions
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30
kernel/signal.c
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@ -911,27 +911,6 @@ __group_complete_signal(int sig, struct task_struct *p)
} while_each_thread(p, t);
return;
}
/*
* There will be a core dump. We make all threads other
* than the chosen one go into a group stop so that nothing
* happens until it gets scheduled, takes the signal off
* the shared queue, and does the core dump. This is a
* little more complicated than strictly necessary, but it
* keeps the signal state that winds up in the core dump
* unchanged from the death state, e.g. which thread had
* the core-dump signal unblocked.
*/
rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
p->signal->group_stop_count = 0;
p->signal->group_exit_task = t;
p = t;
do {
p->signal->group_stop_count++;
signal_wake_up(t, t == p);
} while_each_thread(p, t);
return;
}
/*
@ -1762,15 +1741,6 @@ static int handle_group_stop(void)
{
int stop_count;
if (current->signal->group_exit_task == current) {
/*
* Group stop is so we can do a core dump,
* We are the initiating thread, so get on with it.
*/
current->signal->group_exit_task = NULL;
return 0;
}
if (current->signal->flags & SIGNAL_GROUP_EXIT)
/*
* Group stop is so another thread can do a core dump,