Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sun, 13 Sep 2020 15:55:20 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Souptick Joarder <jrdr.linux@gmail.com>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
Message-ID: <20200913145520.GH6583@casper.infradead.org>
References: <1600007555-11650-1-git-send-email-jrdr.linux@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1600007555-11650-1-git-send-email-jrdr.linux@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> It is possible that a buggy caller of unpin_user_pages()
> (specially in error handling path) may end up calling it with
> npages < 0 which is unnecessary.
> @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
>  {
>  	unsigned long index;
>  
> +	if (WARN_ON_ONCE(npages < 0))
> +		return;

But npages is unsigned long.  So it can't be less than zero.