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

From: Michal Hocko
Date: Wed Oct 08 2014 - 10:08:11 EST

Hi Andrew, Rafael,

this has been originally discussed here [1] but didn't lead anywhere AFAICS
so I would like to resurrect them.

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] http://marc.info/?l=linux-kernel&m=140986986423092
[2] http://marc.info/?l=linux-kernel&m=141074263721166

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