Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH v2 -mm 2/2] current_is_single_threaded: don't use ->mmap_sem | Date | Fri, 10 Jul 2009 15:07:42 +0100 |
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Oleg Nesterov <oleg@redhat.com> wrote:
> current_is_single_threaded() can safely miss a freshly forked CLONE_VM > task, but in this case it must not miss its parent. That is why we take > mm->mmap_sem for writing to make sure a thread/task with the same ->mm > can't pass exit_mm() and disappear. > > However we can avoid ->mmap_sem and rely on rcu/barriers: > > - if we do not see the exiting parent on thread/process list > we see the result of list_del_rcu(), in this case we must > also see the result of list_add_rcu() which does wmb(). > > - if we do see the parent but its ->mm == NULL, we need rmb() > to make sure we can't miss the child. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
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