Date: Tue, 2 Dec 2014 14:35:38 -0500
From: Tejun Heo <tj@kernel.org>
To: Roman Gushchin <klamm@yandex-team.ru>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Li Zefan <lizefan@huawei.com>
Subject: Re: [PATCH 3.10] cgroup: break infinite loop in __css_tryget()
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 <119181417545645@webcorp02h.yandex-team.ru>
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On Tue, Dec 02, 2014 at 09:40:45PM +0300, Roman Gushchin wrote:
> Hi, Tejun!
> 
> 02.12.2014, 19:56, "Tejun Heo" <tj@kernel.org>:
> > Hello, Roman.
> >
> > On Fri, Nov 28, 2014 at 07:47:54PM +0300, Roman Gushchin wrote:
> >> ?If cgroup_destroy_locked() sets the css refcount to a negative value,
> >> ?we get an infinite loop in __css_tryget().
> >>
> >> ?In this case css_refcnt() returns modified (non-negative value), so
> >> ?both (t == v) and (t < 0) conditions are always false.
> >
> > I don't follow. ?The count is biased and modified by unbiasing iff the
> > value is negative. ?Here, @v is the unbiased value and @t is the
> > verbatim value. ?If @v is different from @t due to unbiasing, @t must
> > be negative satisfying the second condition and returning NULL, no?
> 
> Yep. I missed that we compare t with 0 (not v).

Hmm... what's up with the rcu stall message then?

-- 
tejun
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