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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Mon, 24 Oct 2022 10:50:51 +0200
Message-ID: <CAJfpegsciAuJD-UAcW3Ns43G5m1G466opq6_Y6RG1G4iVHwcHQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] kernfs: dont take i_lock on inode attr read
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:
>
> The kernfs write lock is held when the kernfs node inode attributes
> are updated. Therefore, when either kernfs_iop_getattr() or
> kernfs_iop_permission() are called the kernfs node inode attributes
> won't change.
>
> Consequently concurrent kernfs_refresh_inode() calls always copy the
> same values from the kernfs node.
>
> So there's no need to take the inode i_lock to get consistent values
> for generic_fillattr() and generic_permission(), the kernfs read lock
> is sufficient.
>
> Signed-off-by: Ian Kent <raven@themaw.net>

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