linux-kernel - Re: WARNING: lock held when returning to user space in grab

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Message-ID: <20190102161640.GS2509588@devbig004.ftw2.facebook.com>
Date:   Wed, 2 Jan 2019 08:16:40 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Zefan Li <lizefan@...wei.com>,
        syzbot <syzbot+87b93137e0280beaeba1@...kaller.appspotmail.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: WARNING: lock held when returning to user space in grab_super

Happy new year, Tetsuo.

On Wed, Jan 02, 2019 at 09:08:56PM +0900, Tetsuo Handa wrote:
> According to commit 633feee310de6b6c ("cgroup: refactor mount path and
> clearly distinguish v1 and v2 paths"), cgroup_do_mount() is failing to
> do full teardown steps for kernfs_mount() (deactivate_locked_super() ?)
> when kernfs_node_dentry() failed.

Hmm... that's basically dget()'ing the root dentry of the sb.  I'm not
sure how that could fail.  Can it?

Thanks.

-- 
tejun