linux-kernel - Re: [PATCH 1/2] kernfs: dont take i

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Message-ID: <CAJfpegsciAuJD-UAcW3Ns43G5m1G466opq6_Y6RG1G4iVHwcHQ@mail.gmail.com>
Date:   Mon, 24 Oct 2022 10:50:51 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Ian Kent <raven@...maw.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Eric Sandeen <sandeen@...deen.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Rick Lindsley <ricklind@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kernfs: dont take i_lock on inode attr read

On Tue, 18 Oct 2022 at 04:32, Ian Kent <raven@...maw.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@...maw.net>

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