linux-kernel - Re: __blkg_lookup oops with 4.2-rcX

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Date:	Sat, 5 Sep 2015 16:48:40 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Tejun Heo <tj@...nel.org>
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>
Subject: Re: __blkg_lookup oops with 4.2-rcX

On Sat, Sep 05, 2015 at 04:34:39PM +0100, Richard W.M. Jones wrote:
> [   52.259269] BUG: unable to handle kernel NULL pointer dereference at 00000000000009c8
> [   52.259269] IP: [<ffffffff813f8b10>] __blkg_lookup+0x40/0xe0

And also:

$ addr2line -e /usr/lib/debug/lib/modules/4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/vmlinux ffffffff813f8b10
/usr/src/debug/kernel-4.2.fc24/linux-4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/block/blk-cgroup.c:158

    152         /*
    153          * Hint didn't match.  Look up from the radix tree.  Note that the
    154          * hint can only be updated under queue_lock as otherwise @blkg
    155          * could have already been removed from blkg_tree.  The caller is
    156          * responsible for grabbing queue_lock if @update_hint.
    157          */
    158         blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
    159         if (blkg && blkg->q == q) {
    160                 if (update_hint) {
    161                         lockdep_assert_held(q->queue_lock);
    162                         rcu_assign_pointer(blkcg->blkg_hint, blkg);
    163                 }
    164                 return blkg;
    165         }

Rich.

-- 
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