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Ts'o" cc: Dennis Zhou , Jens Axboe , Tejun Heo , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org Subject: Re: [BUG] ext4/block null pointer crashes in linux-next In-reply-to: <20181016015201.GB18547@thunk.org> References: <13987.1539646128@turing-police.cc.vt.edu> <20181016015201.GB18547@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Tue, 16 Oct 2018 08:42:14 -0400 Message-ID: <66480.1539693734@turing-police.cc.vt.edu> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 15 Oct 2018 21:52:01 -0400, "Theodore Y. Ts'o" said: > Given the commit that it bisected down to, I very much doubt it has > anything to do with a specific directory or pathname. Either you or > your distribution has enabled blk cgroup for I/O throttling, and Bingo. [~] zgrep CGROUP /proc/config.gz CONFIG_CGROUPS=y CONFIG_BLK_CGROUP=y # CONFIG_DEBUG_BLK_CGROUP is not set (...) > there's some race that you're tripping across. What ext4 file or > directory happens to be accessed when you trip across the problem is > probably just pure luck. I'm suspecting that my repeatable crash with rpm just does a *really* good job of setting up the race. > If you can disable the block I/O throttling configuration (which may > very well be distro-specific), the problem will probably go away. I > don't use blkcg at all, personally, and on a personal laptop > (especially if you have an SSD), I really don't see the point. I often turn on new features just to watch the sparks fly. > Still, I'm sure the people who *do* use blkcg for real (mostly in data > centers, in my experience) will probably thank you for being a great > guinea pig. :-) It's why I build a linux-next kernel every week. ;) Looks like I should enable DEBUG_BLK_CGROUP and see what that says.