linux-kernel - RE: Bad Reference Semantics in PIDs Controller.

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Message-ID: <CAOviyag1ZOgjtNWmnpfMm=fDgkhDn9UGKoJXy6HLWQMGb-tQAg@mail.gmail.com>
Date:	Sun, 23 Aug 2015 22:24:18 +1000
From:	Aleksa Sarai <cyphar@...har.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: RE: Bad Reference Semantics in PIDs Controller.

It turns out that, actually, the can_attach(), cancel_attach() and
attach() code is broken -- we're incrementing a ref on the old_css of
a task in can_attach(). Then we decrement the ref on a *different* css
(because the task has been migrated). This is clearly a bad thing.
Should we make cgroup_migrate() deal with the accounting for us (by
getting it to grab a ref before can_attach() and dropping it after the
attach succeeds or fails?).

-- 
Aleksa Sarai (cyphar)
www.cyphar.com
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