Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code
Date	2015-06-13 09:30 +0200
Message-ID	<pAO37-611-1@gated-at.bofh.it> (permalink)
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* Oleg Nesterov <oleg@redhat.com> wrote:

> > So we could add tsk->mm_leader or so,
> 
> No, no, please do not. Just do something like
> 
> 	for_each_process(p) {
> 
> 		for_each_thread(p, t) {

So far that's what the for_each_process_thread() iterations I added do, right?

> 			if (t->mm) {
> 				do_something(t->mm);
> 				break;
> 			}
> 		}
> 	}
> 
> But either way I don't understand what protects this ->mm. Perhaps this needs 
> find_lock_task_mm().

That's indeed a bug: I'll add task_lock()/unlock() before looking at ->mm.

find_lock_task_mm() is not needed IMHO: we have a stable reference to 't', as a 
task can only go away via RCU expiry, and all the iterations I added are (supposed 
to) be RCU safe.

Thanks,

	Ingo
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Thread

Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the  Xen guest code Linus Torvalds <torvalds@linux-foundation.org> - 2015-06-11 22:40 +0200
  Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the  Xen guest code Linus Torvalds <torvalds@linux-foundation.org> - 2015-06-11 22:50 +0200
    Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from  the Xen guest code Oleg Nesterov <oleg@redhat.com> - 2015-06-13 01:40 +0200
    Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from  the Xen guest code Ingo Molnar <mingo@kernel.org> - 2015-06-13 09:30 +0200
      Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from  the Xen guest code Oleg Nesterov <oleg@redhat.com> - 2015-06-13 20:10 +0200

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