Messages in this thread | | | Date | Mon, 22 Jun 2009 11:51:48 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] rework/fix is_single_threaded() |
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On Thu, 18 Jun 2009 21:42:38 +0200 Oleg Nesterov <oleg@redhat.com> wrote:
> On 06/18, Andrew Morton wrote: > > > > It appears that this patch is rather stuck. Should I drop it? > > Well, I am biased of course... > > I think the patch is correct. David dislikes down_write(->mmap_sem), > but imho it is better than the global tasklist_lock. > > Looks like we can avoid ->mmap_sem too, but imho this change needs > another patch, it is subtle. > > OTOH, I can't say this patch is important, both the fixed bugs and > improvements are minor. >
hm, that's still all a bit marginal/waffly.
> > > From: Oleg Nesterov <oleg@redhat.com> > > > > - 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.
Maybe we should do the locking change in a separate and subsequent patch?
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