Messages in this thread | | | Date | Mon, 22 Jun 2009 14:04:40 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] rework/fix is_single_threaded() |
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On Mon, 22 Jun 2009 19:14:31 +0200 Oleg Nesterov <oleg@redhat.com> wrote:
> On 06/22, Andrew Morton wrote: > > > > 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? > > Sure, I can split these changes. Or we can just forget about this patch.
noooo the world needs oleg patches.
> > But what is the problem with this patch?
The discussion between yourself and David seems to be unresolved, so I have it in wait-and-see mode.
> David, do you still dislike ->mmap_sem? I didn't see other objections, > and again, imho tasklist_lock is worse.
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