On Monday, September 08, 2014 01:58:30 PM Cong Wang wrote: > On Mon, Sep 8, 2014 at 1:54 PM, Rafael J. Wysocki <r...@rjwysocki.net> wrote: > > On Monday, September 08, 2014 10:40:17 AM Cong Wang wrote: > >> > >> We asked you to comment on either if this patch is safe for PM freeze > >> if we don't have the cgroup_freezing() check, or if it is not safe why (so > >> that > >> I can put it in the comment). > > > > OK, which version of it? Anything that has been posted as a complete patch > > you > > have a link to? Or am I supposed to go through the whole thread and figure > > out > > how the patch *might* have looked had it been posted and then comment? > > Sorry, I meant this version, the one we are discussing about. > In case you missed it too, let me show the related code for you: > > + /* It might not be safe to check TIF_MEMDIE for pm freeze. */ > + if (cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE)) > + return true; > + > > (return true means it will break the loop of freezing, that is thaw itself.) > > So our question is if we really need the cgroup_freezing() check here?
No, I don't think so. > IOW, is it safe to check TIF_MEMDIE and then thaw itself even if the > freeze request is from PM? Hope it is clear now. Yes, it is clear, thanks. Why would the cgroup_freezing() test matter here at all? > >> OK, maybe just one or two sentences. Let me know if the following > >> comment is okay for you: > >> > >> /* OOM killer might decide to kill this process after it is frozen, > >> in this case it should thaw and die. */ > > > > I don't think it's sufficient. In particular, what does "thaw and die" mean > > exactly? It should be thawed immediately and then die or it should die > > right > > after it's thawed (at one point in the future)? > > > > OK, let me try again: > > /* OOM killer may decide to kill this process after it is frozen, > in this case SIGKILL can never be handled, so we should check > TIF_MEMDIE and if it is set, thaw and let SIGKILL kill it. */ > > (Again, more detailed explanation is in the changelog, comment is just > for a quick reference, this seems what we all agree on.) OK I think you can simply add the test_thread_flag(TIF_MEMDIE) check to __refrigerator() and it should be OK without the comment. But please tell me this: If TIF_MEMDIE is set and we thaw the process, can it do *anything* before dying or will it die immediately? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
