Re: do_syslog/__down_trylock lockup in current BK

From: Ingo Molnar (mingo@elte.hu)
Date: Mon Sep 09 2002 - 15:33:17 EST

the attached patch fixes one bug in the way we did zap_thread() - but this
alone does not fix the lockup.

the bug was that list_for_each_safe() is not 'safe enough' - zap_thread()
drops the tasklist lock at which point anything might happen to the child
list.

the lockup is likely in the while loop - ie. zap_thread() not actually
reparenting a thread and thus causing an infinite loop - is that possible?

        Ingo

--- linux/kernel/exit.c.orig Mon Sep 9 21:59:24 2002
+++ linux/kernel/exit.c Mon Sep 9 22:24:41 2002
@@ -493,7 +493,6 @@
 static void exit_notify(void)
 {
         struct task_struct *t;
- struct list_head *_p, *_n;
 
         forget_original_parent(current);
         /*
@@ -554,17 +553,16 @@
                 do_notify_parent(current, current->exit_signal);
 
 zap_again:
- list_for_each_safe(_p, _n, &current->children)
- zap_thread(list_entry(_p,struct task_struct,sibling), current, 0);
- list_for_each_safe(_p, _n, &current->ptrace_children)
- zap_thread(list_entry(_p,struct task_struct,ptrace_list), current, 1);
+ while (!list_empty(&current->children))
+ zap_thread(list_entry(current->children.next,struct task_struct,sibling), current, 0);
+ while (!list_empty(&current->ptrace_children))
+ zap_thread(list_entry(current->ptrace_children.next,struct task_struct,sibling), current, 0);
         /*
          * zap_thread might drop the tasklist lock, thus we could
          * have new children queued back from the ptrace list into the
          * child list:
          */
- if (unlikely(!list_empty(&current->children) ||
- !list_empty(&current->ptrace_children)))
+ if (unlikely(!list_empty(&current->children)))
                 goto zap_again;
         /*
          * No need to unlock IRQs, we'll schedule() immediately

-
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This archive was generated by hypermail 2b29 : Sun Sep 15 2002 - 22:00:18 EST