Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 12 Dec 2022 08:22:26 -0500
From:   Brian Foster <bfoster@redhat.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Nhat Pham <nphamcs@gmail.com>, akpm@linux-foundation.org,
        hannes@cmpxchg.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, willy@infradead.org,
        kernel-team@meta.com
Subject: Re: [PATCH v2 3/4] cachestat: implement cachestat syscall
Message-ID: <Y5crEpr5QWptjK17@bfoster>
References: <20221205175140.1543229-1-nphamcs@gmail.com>
 <20221205175140.1543229-4-nphamcs@gmail.com>
 <Y5UbhBTB2nSMN4UD@ZenIV>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y5UbhBTB2nSMN4UD@ZenIV>
Precedence: bulk

On Sat, Dec 10, 2022 at 11:51:32PM +0000, Al Viro wrote:
> On Mon, Dec 05, 2022 at 09:51:39AM -0800, Nhat Pham wrote:
> 
> > +	if (!access_ok(cstat, sizeof(struct cachestat)))
> > +		return -EFAULT;
> 
> What for?  You are using copy_to_user() later, right?
> 
> > +	f = fdget(fd);
> > +	if (f.file) {
> 
> It would be easier to read if you inverted the condition here.
> 

Seconded.. I mentioned the same the last time I looked at this. On
looking again, perhaps it might even make sense to create a
filemap_cachestat() to split up the syscall bits from the associated map
walking bits..? That subsequently raises the question of whether a new
.c file is really necessary..

Brian