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

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Message-ID: <Y2BMonmS0SdOn5yh@slm.duckdns.org>
Date:   Mon, 31 Oct 2022 12:30:58 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Ian Kent <raven@...maw.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.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>,
        Miklos Szeredi <miklos@...redi.hu>,
        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, Oct 18, 2022 at 10:32:42AM +0800, Ian Kent 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>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun