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SubjectRe: doublefault debugging (was Re: Linux v2.5.62 --- spontaneous reboots)

On Thu, 20 Feb 2003, Linus Torvalds wrote:

> > ie. something like:
>
> Well, please remove the double test for task inequality.

ok.

> I like the patch conceptually, HOWEVER, I'm not sure it's correct. The
> thing is, moving the wait_task_inactive() to __put_task_struct() means
> that we will be doing the "release_task()" teardown while the task is
> still potentially active on another CPU.
>
> In particular, we'll be freeing the security stuff and the signals while
> the process may still be active in the scheduler on another CPU. This
> can be dangerous, ie doing things like calling "free_uid()" on a process
> that is still running means that suddenly you have issues like not being
> able to trust "current->user" from interrupts. We may not care right
> now, but it's still wrong (imagine us doing per-user time accounting -
> which makes a _lot_ of sense).

well, we can do the wait_task_inactive() in both cases - in
release_task(), and in __put_task_struct(). [in the release_task() path
that will just be a nop]. This further simplifies the patch.

Ingo

--- kernel/fork.c.orig
+++ kernel/fork.c
@@ -75,6 +75,7 @@
void __put_task_struct(struct task_struct *tsk)
{
if (tsk != current) {
+ wait_task_inactive(tsk);
free_thread_info(tsk->thread_info);
kmem_cache_free(task_struct_cachep,tsk);
} else {
-
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