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authorOleg Nesterov <oleg@tv-sign.ru>2005-10-07 17:46:19 +0400
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-08 14:53:31 -0700
commit788e05a67c343fa22f2ae1d3ca264e7f15c25eaf (patch)
tree4fa2f7e11cc757160ae5f492fdbe0da72d30cf26
parent829841146878e082613a49581ae252c071057c23 (diff)
[PATCH] fix do_coredump() vs SIGSTOP race
Let's suppose we have 2 threads in thread group: A - does coredump B - has pending SIGSTOP thread A thread B do_coredump: get_signal_to_deliver: lock(->sighand) ->signal->flags = SIGNAL_GROUP_EXIT unlock(->sighand) lock(->sighand) signr = dequeue_signal() ->signal->flags |= SIGNAL_STOP_DEQUEUED return SIGSTOP; do_signal_stop: unlock(->sighand) coredump_wait: zap_threads: lock(tasklist_lock) send SIGKILL to B // signal_wake_up() does nothing unlock(tasklist_lock) lock(tasklist_lock) lock(->sighand) re-check sig->flags & SIGNAL_STOP_DEQUEUED, yes set_current_state(TASK_STOPPED); finish_stop: schedule(); // ->state == TASK_STOPPED wait_for_completion(&startup_done) // waits for complete() from B, // ->state == TASK_UNINTERRUPTIBLE We can't wake up 'B' in any way: SIGCONT will be ignored because handle_stop_signal() sees ->signal->flags & SIGNAL_GROUP_EXIT. sys_kill(SIGKILL)->__group_complete_signal() will choose uninterruptible 'A', so it can't help. sys_tkill(B, SIGKILL) will be ignored by specific_send_sig_info() because B already has pending SIGKILL. This scenario is not possbile if 'A' does do_group_exit(), because it sets sig->flags = SIGNAL_GROUP_EXIT and delivers SIGKILL to subthreads atomically, holding both tasklist_lock and sighand->lock. That means that do_signal_stop() will notice !SIGNAL_STOP_DEQUEUED after re-locking ->sighand. And it is not possible to any other thread to re-add SIGNAL_STOP_DEQUEUED later, because dequeue_signal() can only return SIGKILL. I think it is better to change do_coredump() to do sigaddset(SIGKILL) and signal_wake_up() under sighand->lock, but this patch is much simpler. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/signal.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index 619b027e92b5..c135f5aa2c2d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -578,7 +578,8 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
* is to alert stop-signal processing code when another
* processor has come along and cleared the flag.
*/
- tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
+ if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
+ tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
}
if ( signr &&
((info->si_code & __SI_MASK) == __SI_TIMER) &&

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