linux-kernel - Re: [PATCH] device_cgroup: fix RCU imbalance in error case

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Message-ID: <20190319174725.GA69236@devbig004.ftw2.facebook.com>
Date:   Tue, 19 Mar 2019 10:47:25 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Aristeu Rozanski <aris@...hat.com>,
        "Serge E . Hallyn" <serge.hallyn@...ntu.com>,
        Michal Hocko <mhocko@...e.cz>, cgroups@...r.kernel.org
Subject: Re: [PATCH] device_cgroup: fix RCU imbalance in error case

On Tue, Mar 19, 2019 at 02:36:59AM +0100, Jann Horn wrote:
> When dev_exception_add() returns an error (due to a failed memory
> allocation), make sure that we move the RCU preemption count back to where
> it was before we were called. We dropped the RCU read lock inside the loop
> body, so we can't just "break".
> 
> sparse complains about this, too:
> 
> $ make -s C=2 security/device_cgroup.o
> ./include/linux/rcupdate.h:647:9: warning: context imbalance in
> 'propagate_exception' - unexpected unlock
> 
> Fixes: d591fb56618f ("device_cgroup: simplify cgroup tree walk in propagate_exception()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jann Horn <jannh@...gle.com>

Applied to cgroup/for-5.1-fixes.

Thanks.

-- 
tejun