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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Mon, 24 Oct 2022 10:38:05 +0200
Message-ID: <CAJfpegts1pqM1Qi4sEAB22W1qBzZaAkgpY+LjBp65=Ns+KHB3w@mail.gmail.com>
Subject: Re: [PATCH 2/2] kernfs: dont take i_lock on revalidate
To:     Ian Kent <raven@themaw.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Minchan Kim <minchan@kernel.org>,
        Eric Sandeen <sandeen@sandeen.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Rick Lindsley <ricklind@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Carlos Maiolino <cmaiolino@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, 18 Oct 2022 at 04:32, Ian Kent <raven@themaw.net> wrote:
>
> In kernfs_dop_revalidate() when the passed in dentry is negative the
> dentry directory is checked to see if it has changed and if so the
> negative dentry is discarded so it can refreshed. During this check
> the dentry inode i_lock is taken to mitigate against a possible
> concurrent rename.
>
> But if it's racing with a rename, becuase the dentry is negative, it
> can't be the source it must be the target and it must be going to do
> a d_move() otherwise the rename will return an error.
>
> In this case the parent dentry of the target will not change, it will
> be the same over the d_move(), only the source dentry parent may change
> so the inode i_lock isn't needed.
>
> Signed-off-by: Ian Kent <raven@themaw.net>

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>