linux-kernel - Re: [PATCH] kernfs: don't create a negative dentry if inactive node exists

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Date:   Wed, 29 Sep 2021 08:05:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ian Kent <raven@...maw.net>
Cc:     Tejun Heo <tj@...nel.org>, Hou Tao <houtao1@...wei.com>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Rick Lindsley <ricklind@...ux.vnet.ibm.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernfs: don't create a negative dentry if inactive node
 exists

On Wed, Sep 29, 2021 at 11:04:34AM +0800, Ian Kent wrote:
> In kernfs_iop_lookup() a negative dentry is created if there's no kernfs
> node associated with the dentry or the node is inactive.
> 
> But inactive kernfs nodes are meant to be invisible to the VFS and
> creating a negative dentry for these can have unexpected side effects
> when the node transitions to an active state.
> 
> The point of creating negative dentries is to avoid the expensive
> alloc/free cycle that occurs if there are frequent lookups for kernfs
> attributes that don't exist. So kernfs nodes that are not yet active
> should not result in a negative dentry being created so when they
> transition to an active state VFS lookups can create an associated
> dentry is a natural way.
> 
> Signed-off-by: Ian Kent <raven@...maw.net>
> ---
>  fs/kernfs/dir.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

Does this fix a specific commit and need a "Fixes:" tag?

thanks,

greg k-h