Re: [patch] Re: Problem with exiting threads under NPTL

Ingo Molnar
2003-12-14T22:29:29Z

here's yet another variant of the patch. Changes relative to yours:

- it sets zap_leader to 0 outside the critical section.

- it doesnt set leader to TASK_DEAD, exit_signal == -1 should really
protect it from sys_wait4() i believe.

- it sets 'p = leader' within the unlikely branch - slightly faster common
case.

the patch testbooted fine here.

Ingo

--- linux/kernel/exit.c.orig
+++ linux/kernel/exit.c
@@ -50,8 +50,11 @@ static void __unhash_process(struct task
void release_task(struct task_struct * p)
{
task_t *leader;
+ int zap_leader;
struct dentry *proc_dentry;
-
+
+repeat:
+ zap_leader = 0;
BUG_ON(p->state < TASK_ZOMBIE);

atomic_dec(&p->user->processes);
@@ -72,8 +75,16 @@ void release_task(struct task_struct * p
*/
leader = p->group_leader;
if (leader != p && thread_group_empty(leader) &&
- leader->state == TASK_ZOMBIE && leader->exit_signal != -1)
+ leader->state == TASK_ZOMBIE && leader->exit_signal != -1) {
do_notify_parent(leader, leader->exit_signal);
+ /*
+ * If we were the last child thread and the leader has
+ * exited already, and the leader's parent ignores SIGCHLD,
+ * then we are the one who should release the leader.
+ */
+ if (leader->exit_signal == -1)
+ zap_leader = 1;
+ }

p->parent->cutime += p->utime + p->cutime;
p->parent->cstime += p->stime + p->cstime;
@@ -88,6 +99,16 @@ void release_task(struct task_struct * p
proc_pid_flush(proc_dentry);
release_thread(p);
put_task_struct(p);
+
+ /*
+ * Do this outside the tasklist lock. The reference to the
+ * leader is safe. There's no recursion possible, since
+ * the leader of the leader is itself:
+ */
+ if (unlikely(zap_leader)) {
+ p = leader;
+ goto repeat;
+ }
}

/* we are using it only for SMP init */