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SubjectRe: [PATCH] rework/fix is_single_threaded()
On Mon, 13 Apr 2009 23:45:13 +0200
Oleg Nesterov <oleg@redhat.com> wrote:

> - Fix the comment, is_single_threaded(p) actually means that nobody shares
> ->mm with p.
>
> I think this helper should be renamed, and it should not have arguments.
> With or without this patch it must not be used unless p == current,
> otherwise we can't safely use p->signal or p->mm.
>
> - "if (atomic_read(&p->signal->count) != 1)" is not right when we have a
> zombie group leader, use signal->live instead.
>
> - Add PF_KTHREAD check to skip kernel threads which may borrow p->mm,
> otherwise we can return the wrong "false".
>
> - Use for_each_process() instead of do_each_thread(), all threads must use
> the same ->mm.
>
> - Use down_write(mm->mmap_sem) + rcu_read_lock() instead of tasklist_lock
> to iterate over the process list. If there is another CLONE_VM process
> it can't pass exit_mm() which takes the same mm->mmap_sem. We can miss
> a freshly forked CLONE_VM task, but this doesn't matter because we must
> see its parent and return false.

hum. I'm searching for a reason to merge this into 2.6.30 but I'm not
seeing one?



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