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Date:   Wed, 4 Sep 2019 11:39:58 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     "Weiny, Ira" <ira.weiny@intel.com>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        zhong jiang <zhongjiang@huawei.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "mhocko@kernel.org" <mhocko@kernel.org>,
        "anshuman.khandual@arm.com" <anshuman.khandual@arm.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero
Message-ID: <20190904183958.GM29434@bombadil.infradead.org>
References: <1567592763-25282-1-git-send-email-zhongjiang@huawei.com>
 <5505fa16-117e-8890-0f48-38555a61a036@suse.cz>
 <2807E5FD2F6FDA4886F6618EAC48510E898E9559@CRSMSX101.amr.corp.intel.com>
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On Wed, Sep 04, 2019 at 06:25:19PM +0000, Weiny, Ira wrote:
> > On 9/4/19 12:26 PM, zhong jiang wrote:
> > > With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> > > compare with zero. And __get_user_pages_locked will return an long
> > value.
> > > Hence, Convert the long to compare with zero is feasible.
> > 
> > It would be nicer if the parameter nr_pages was long again instead of
> > unsigned long (note there are two variants of the function, so both should be
> > changed).
> 
> Why?  What does it mean for nr_pages to be negative?  The check below seems valid.  Unsigned can be 0 so the check can fail.  IOW Checking unsigned > 0 seems ok.
> 
> What am I missing?

__get_user_pages can return a negative errno.