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Date: Wed, 2 Jan 2019 20:02:23 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Andrei Vagin <avagin@gmail.com>
Cc: David Howells <dhowells@redhat.com>, linux-fsdevel@vger.kernel.org,
        cgroups@vger.kernel.org, Li Zefan <lizefan@huawei.com>
Subject: Re: [PATCH vfs/for-next v4] cgroup: fix top cgroup refcnt leak
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 <20190102193756.6096-1-avagin@gmail.com>
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On Wed, Jan 02, 2019 at 11:37:56AM -0800, Andrei Vagin wrote:
> +	if (unlikely(ret)) {
> +		dput(fc->root);
> +		deactivate_locked_super(fc->root->d_sb);
> +		fc->root = NULL;

Er...  I'd rather not dereference the damn thing after dput().
It's _probably_ OK (fc->root here, AFAICS, is going to be
equal to its ->sb->s_root, and thus still pinned), but it's
better to fetch ->d_sb first.  If nothing else, it's easier
to prove correctness that way...