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SubjectRe: do_syslog/__down_trylock lockup in current BK

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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