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Date: Sun, 4 Sep 2016 15:06:07 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Dmitry Vyukov <dvyukov@google.com>
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Subject: Re: fs: GPF in bd_mount
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On Sun, Sep 04, 2016 at 12:43:28PM +0200, Dmitry Vyukov wrote:

AFAICS, it's been introduced in commit 3684aa7099e0ab1038a1a1bf717ae60ffc3018d1
Author: Shaohua Li <shli@fb.com>
Date:   Mon Feb 22 15:27:40 2016 -0700

    block-dev: enable writeback cgroup support

See if you can reproduce it after the following:

ed fs/block_dev.c <<'EOF'
/bd_mount/
/if/s/dent/!IS_ERR(dent)/
wq
EOF

Said that, I'm not sure why mount_pseudo() would be returning any errors;
rejection should happen in the caller (due to MS_NOUSER in the flags), but
I don't understand what would trigger it on mount_pseudo() level...