Re: [PATCH 0/3] OOM vs. freezer interaction fixes

From: Rafael J. Wysocki
Date: Wed Oct 08 2014 - 17:51:29 EST

On Wednesday, October 08, 2014 04:07:43 PM Michal Hocko wrote:
> Hi Andrew, Rafael,
> this has been originally discussed here [1] but didn't lead anywhere AFAICS
> so I would like to resurrect them.


So any chance to CC linux-pm too next time? There are people on that list
who may be interested as well and are not in the CC directly either.

> The first and third patch are regression fixes and they are a stable
> material IMO. The second patch is a simple cleanup.
> The 1st patch is fixing a regression introduced in 3.3 since when OOM
> killer is not able to kill any frozen task and live lock as a result.
> The fix gets us back to the 3.2. As it turned out during the discussion [2]
> this was still not 100% sufficient and that's why we need the 3rd patch.
> I was thinking about the proper 1st vs. 3rd patch ordering because
> the 1st patch basically opens a race window fixed by the later patch.
> Original patch from Cong Wang has covered this by cgroup_freezing(current)
> check in should_thaw_current(). But this approach still suffers from OOM
> vs. PM freezer interaction (OOM killer would still live lock waiting for a
> PM frozen task this time).
> So I think the most straight forward way is to address only OOM vs.
> frozen task interaction in the first patch, mark it for stable 3.3+ and
> leave the race to a separate follow up patch which is applicable to
> stable 3.2+ (before a3201227f803 made it inefficient).
> Switching 1st and 3rd patches would make some sense as well but then
> it might end up even more confusing because we would be fixing a
> non-existent issue in upstream first...
> ---
> [1]
> [2]

I'm fine with the approach in general, but I need to stare at patch 3
for a little bit longer before I ACK it. Which may not happen really
soon as I'll be rather busy on Thu/Fri and then I'll be traveling to
the LPC/LCEU next week.

I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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