linux-kernel - Re: [PATCH block/for-linus] block: blkg_destroy_all() should clear q->root_blkg and ->root

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Date:	Tue, 8 Sep 2015 11:31:32 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Jeff Moyer <jmoyer@...hat.com>, msnitzer@...hat.com,
	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	"Richard W.M. Jones" <rjones@...hat.com>
Subject: Re: [PATCH block/for-linus] block: blkg_destroy_all() should clear
 q->root_blkg and ->root_rl.blkg

On Sat, Sep 05, 2015 at 03:47:36PM -0400, Tejun Heo wrote:
> While making the root blkg unconditional, ec13b1d6f0a0 ("blkcg: always
> create the blkcg_gq for the root blkcg") removed the part which clears
> q->root_blkg and ->root_rl.blkg during q exit.  This leaves the two
> pointers dangling after blkg_destroy_all().  blk-throttle exit path
> performs blkg traversals and dereferences ->root_blkg and can lead to
> the following oops.

Jens, can you please route this one w/ Richard's tested-by added?

Thanks!

-- 
tejun
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