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

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Message-ID: <20190102165528.GT2509588@devbig004.ftw2.facebook.com>
Date:   Wed, 2 Jan 2019 08:55:28 -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

On Thu, Jan 03, 2019 at 01:49:55AM +0900, Tetsuo Handa wrote:
> kernfs_node_dentry() calls lookup_one_len_unlocked() which involves
> memory allocation, and memory allocation fault injection made
> lookup_one_len_unlocked() fail, and thus kernfs_node_dentry() failed.
> What's strange?

So, kernfs_node_dentry() is called on the root kn, which should
trigger "if (!kn->parent) return dentry" in kernfs_node_dentry(), so
it shouldn't reach lookup_on_len_unlocked().  Oh I see.  This is the
namespaced mount path, so kn can be non-root.  Will fix it.

Thanks.

-- 
tejun