Re: [PATCH] [RFC] fix missed SIGCONT cases

From: Oleg Nesterov
Date: Mon Mar 03 2008 - 08:21:23 EST

Actually, it is easy to re-use signal_struct->flags from the very beginning,
no need to introduce the new flag temporary, see the attached patches. I also
have a couple of simple cleanups on top of them (use cached ->signal value).

Perhaps, we can add the new helper which sets SIGNAL_GROUP_EXIT but preserves
SIGNAL_CLD_MASK, but I don't think this is really needed.

Oleg.
--- 25/include/linux/sched.h~1_SIGCONT_IMPL 2008-02-17 23:40:09.000000000 +0300
+++ 25/include/linux/sched.h 2008-03-03 13:40:14.000000000 +0300
@@ -555,6 +555,12 @@ struct signal_struct {
#define SIGNAL_STOP_DEQUEUED 0x00000002 /* stop signal dequeued */
#define SIGNAL_STOP_CONTINUED 0x00000004 /* SIGCONT since WCONTINUED reap */
#define SIGNAL_GROUP_EXIT 0x00000008 /* group exit in progress */
+/*
+ * Pending notifications to parent.
+ */
+#define SIGNAL_CLD_STOPPED 0x00000010
+#define SIGNAL_CLD_CONTINUED 0x00000020
+#define SIGNAL_CLD_MASK (SIGNAL_CLD_STOPPED|SIGNAL_CLD_CONTINUED)

/* If true, all threads except ->group_exit_task have pending SIGKILL */
static inline int signal_group_exit(const struct signal_struct *sig)
--- 25/kernel/signal.c~1_SIGCONT_IMPL 2008-02-17 23:40:09.000000000 +0300
+++ 25/kernel/signal.c 2008-03-03 13:51:55.000000000 +0300
@@ -595,10 +595,8 @@ static void handle_stop_signal(int sig,
* the SIGCHLD was pending on entry to this kill.
*/
p->signal->group_stop_count = 0;
- p->signal->flags = SIGNAL_STOP_CONTINUED;
- spin_unlock(&p->sighand->siglock);
- do_notify_parent_cldstop(p, CLD_STOPPED);
- spin_lock(&p->sighand->siglock);
+ p->signal->flags = SIGNAL_STOP_CONTINUED |
+ SIGNAL_CLD_STOPPED;
}
rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
t = p;
@@ -635,25 +633,23 @@ static void handle_stop_signal(int sig,
* We were in fact stopped, and are now continued.
* Notify the parent with CLD_CONTINUED.
*/
- p->signal->flags = SIGNAL_STOP_CONTINUED;
+ p->signal->flags = SIGNAL_STOP_CONTINUED |
+ SIGNAL_CLD_CONTINUED;
p->signal->group_exit_code = 0;
- spin_unlock(&p->sighand->siglock);
- do_notify_parent_cldstop(p, CLD_CONTINUED);
- spin_lock(&p->sighand->siglock);
} else {
/*
* We are not stopped, but there could be a stop
* signal in the middle of being processed after
* being removed from the queue. Clear that too.
*/
- p->signal->flags = 0;
+ p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
}
} else if (sig == SIGKILL) {
/*
* Make sure that any pending stop signal already dequeued
* is undone by the wakeup for SIGKILL.
*/
- p->signal->flags = 0;
+ p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
}
}

@@ -1761,6 +1757,19 @@ int get_signal_to_deliver(siginfo_t *inf

relock:
spin_lock_irq(&current->sighand->siglock);
+
+ if (unlikely(current->signal->flags & SIGNAL_CLD_MASK)) {
+ int why = (current->signal->flags & SIGNAL_STOP_CONTINUED)
+ ? CLD_CONTINUED : CLD_STOPPED;
+ current->signal->flags &= ~SIGNAL_CLD_MASK;
+ spin_unlock_irq(&current->sighand->siglock);
+
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current->group_leader, why);
+ read_unlock(&tasklist_lock);
+ goto relock;
+ }
+
for (;;) {
struct k_sigaction *ka;

--- 25/kernel/signal.c~2_HSS_SIMPLIFY 2008-03-03 13:51:55.000000000 +0300
+++ 25/kernel/signal.c 2008-03-03 14:47:39.000000000 +0300
@@ -577,33 +577,16 @@ static void handle_stop_signal(int sig,
t = next_thread(t);
} while (t != p);
} else if (sig == SIGCONT) {
+ unsigned int why;
/*
* Remove all stop signals from all queues,
* and wake all threads.
*/
- if (unlikely(p->signal->group_stop_count > 0)) {
- /*
- * There was a group stop in progress. We'll
- * pretend it finished before we got here. We are
- * obliged to report it to the parent: if the
- * SIGSTOP happened "after" this SIGCONT, then it
- * would have cleared this pending SIGCONT. If it
- * happened "before" this SIGCONT, then the parent
- * got the SIGCHLD about the stop finishing before
- * the continue happened. We do the notification
- * now, and it's as if the stop had finished and
- * the SIGCHLD was pending on entry to this kill.
- */
- p->signal->group_stop_count = 0;
- p->signal->flags = SIGNAL_STOP_CONTINUED |
- SIGNAL_CLD_STOPPED;
- }
rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
t = p;
do {
unsigned int state;
rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
-
/*
* If there is a handler for SIGCONT, we must make
* sure that no thread returns to user mode before
@@ -613,7 +596,7 @@ static void handle_stop_signal(int sig,
* running the handler. With the TIF_SIGPENDING
* flag set, the thread will pause and acquire the
* siglock that we hold now and until we've queued
- * the pending signal.
+ * the pending signal.
*
* Wake up the stopped thread _after_ setting
* TIF_SIGPENDING
@@ -628,13 +611,23 @@ static void handle_stop_signal(int sig,
t = next_thread(t);
} while (t != p);

- if (p->signal->flags & SIGNAL_STOP_STOPPED) {
- /*
- * We were in fact stopped, and are now continued.
- * Notify the parent with CLD_CONTINUED.
- */
- p->signal->flags = SIGNAL_STOP_CONTINUED |
- SIGNAL_CLD_CONTINUED;
+ /*
+ * Notify the parent with CLD_CONTINUED if we were stopped.
+ *
+ * If we were in the middle of a group stop, we pretend it
+ * was already finished, and then continued. Since SIGCHLD
+ * doesn't queue we report only CLD_STOPPED, as if the next
+ * CLD_CONTINUED was dropped.
+ */
+ why = 0;
+ if (p->signal->flags & SIGNAL_STOP_STOPPED)
+ why |= SIGNAL_CLD_CONTINUED;
+ else if (p->signal->group_stop_count)
+ why |= SIGNAL_CLD_STOPPED;
+
+ if (why) {
+ p->signal->flags = why | SIGNAL_STOP_CONTINUED;
+ p->signal->group_stop_count = 0;
p->signal->group_exit_code = 0;
} else {
/*