Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <166606025456.13363.3829702374064563472.stgit@donald.themaw.net> <166606036967.13363.9336408133975631967.stgit@donald.themaw.net>
In-Reply-To: <166606036967.13363.9336408133975631967.stgit@donald.themaw.net>
From:   Amir Goldstein <amir73il@gmail.com>
Date:   Tue, 1 Nov 2022 09:46:48 +0200
Message-ID: <CAOQ4uxjiEbHwT7M1GhPb_GFn-oiuvqwS1aOw7N9N8cu5jam5Yw@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>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Carlos Maiolino <cmaiolino@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, Oct 18, 2022 at 5:58 AM 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.

You meant d_lock.
Same for the commit title.

Thanks,
Amir.