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authorOleg Nesterov <oleg@tv-sign.ru>2008-02-08 04:19:12 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-08 09:22:27 -0800
commitd12619b5ff5664623524aef796514d1946ea3b4a (patch)
tree23140ca0148f9154440d3056e2040d8df468a24b
parent430c623121ea88ca80595c99fdc63b7f8a803ae5 (diff)
fix group stop with exit race
do_signal_stop() counts all sub-thread and sets ->group_stop_count accordingly. Every thread should decrement ->group_stop_count and stop, the last one should notify the parent. However a sub-thread can exit before it notices the signal_pending(), or it may be somewhere in do_exit() already. In that case the group stop never finishes properly. Note: this is a minimal fix, we can add some optimizations later. Say we can return quickly if thread_group_empty(). Also, we can move some signal related code from exit_notify() to exit_signals(). Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Davide Libenzi <davidel@xmailserver.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/signal.h1
-rw-r--r--kernel/exit.c2
-rw-r--r--kernel/signal.c27
3 files changed, 28 insertions, 2 deletions
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 7e095147656..42d2e0a948f 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -241,6 +241,7 @@ extern int show_unhandled_signals;
struct pt_regs;
extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
+extern void exit_signals(struct task_struct *tsk);
extern struct kmem_cache *sighand_cachep;
diff --git a/kernel/exit.c b/kernel/exit.c
index d7815f57088..8f3bf53a5b4 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -947,7 +947,7 @@ fastcall NORET_TYPE void do_exit(long code)
schedule();
}
- tsk->flags |= PF_EXITING;
+ exit_signals(tsk); /* sets PF_EXITING */
/*
* tsk->flags are checked in the futex code to protect against
* an exiting task cleaning up the robust pi futexes.
diff --git a/kernel/signal.c b/kernel/signal.c
index 3fca710a5cd..209eec11eef 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1739,7 +1739,7 @@ static int do_signal_stop(int signr)
* stop is always done with the siglock held,
* so this check has no races.
*/
- if (!t->exit_state &&
+ if (!(t->flags & PF_EXITING) &&
!task_is_stopped_or_traced(t)) {
stop_count++;
signal_wake_up(t, 0);
@@ -1900,6 +1900,31 @@ relock:
return signr;
}
+void exit_signals(struct task_struct *tsk)
+{
+ int group_stop = 0;
+
+ spin_lock_irq(&tsk->sighand->siglock);
+ if (unlikely(tsk->signal->group_stop_count) &&
+ !--tsk->signal->group_stop_count) {
+ tsk->signal->flags = SIGNAL_STOP_STOPPED;
+ group_stop = 1;
+ }
+
+ /*
+ * From now this task is not visible for group-wide signals,
+ * see wants_signal(), do_signal_stop().
+ */
+ tsk->flags |= PF_EXITING;
+ spin_unlock_irq(&tsk->sighand->siglock);
+
+ if (unlikely(group_stop)) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(tsk, CLD_STOPPED);
+ read_unlock(&tasklist_lock);
+ }
+}
+
EXPORT_SYMBOL(recalc_sigpending);
EXPORT_SYMBOL_GPL(dequeue_signal);
EXPORT_SYMBOL(flush_signals);