linux-kernel - Re: [PATCH 06/06] 9p fid refcount: cleanup p9_fid

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Date:   Mon, 13 Jun 2022 15:12:41 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Christian Schoenebeck <linux_oss@...debyte.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>,
        v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/06] 9p fid refcount: cleanup p9_fid_put calls

On 2022-06-14 04:50:45, Dominique Martinet wrote:
> Thanks for the reviews,
> 
> Tyler Hicks wrote on Mon, Jun 13, 2022 at 12:55:09PM -0500:
> > > @@ -189,13 +197,13 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
> > >  		else
> > >  			uname = v9ses->uname;
> > >  
> > > -		root_fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
> > > -					    v9ses->aname);
> > > -		if (IS_ERR(root_fid))
> > > -			return root_fid;
> > > +		fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
> > 
> > To keep the readability benefits in my "9p: Track the root fid with its
> > own variable during lookups" patch, I think root_fid should be assigned
> > here and then used in the error check and return statement.
> > 
> > > +				       v9ses->aname);
> > > +		if (IS_ERR(fid))
> > > +			return fid;
> > >  
> > > -		p9_fid_get(root_fid);
> > > -		v9fs_fid_add(dentry->d_sb->s_root, root_fid);
> > > +		root_fid = p9_fid_get(fid);
> > > +		v9fs_fid_add(dentry->d_sb->s_root, &fid);
> > 
> > root_fid should be used in the two lines above, too.
> 
> This actually was the only place where we still want to use the root_fid
> after calling v9fs_fid_add; if we keep root_fid above we need to do
> something like
> 
> fid = p9_fid_get(root_fid);
> v9fs_Fid_add(dentry->d_sb->s_root, &root_fid);
> root_fid = fid;
> // fid = NULL; ? not strictly needed as we set it again shortly afterwards
> 
> which I wanted to avoid, but I guess I don't mind strongly either way --
> pick your poison.

Ah, very good point. I missed that subtly.

> I could also just keep v9fs_fid_add as a non-stealing version, but I
> think it's better that way as it strongly signal that we stashed that
> ref away and shouldn't use the fid anymore unless another ref was
> obtained through fid_get like we do here.
> (I was actually tempted to do the same with p9_fid_put, but checking
> other kernel "put"s I didn't see any code that does this so I refrained
> from that churn)

I like the stealing version. Lets go with it and keep this patch as-is.

Please feel free to slap this tag on it:

 Reviewed-by: Tyler Hicks <tyhicks@...ux.microsoft.com>


Tyler

> 
> -- 
> Dominique
>