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[195.135.220.15]) by mx.google.com with ESMTPS id 20si8219589edx.64.2019.04.11.01.19.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Apr 2019 01:19:01 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3F6C4AD65; Thu, 11 Apr 2019 08:19:01 +0000 (UTC) Date: Thu, 11 Apr 2019 10:19:00 +0200 From: Michal Hocko To: Yufen Yu Cc: mike.kravetz@oracle.com, linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com Subject: Re: [PATCH v2] hugetlbfs: fix protential null pointer dereference Message-ID: <20190411081900.GP10383@dhcp22.suse.cz> References: <20190411035318.32976-1-yuyufen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190411035318.32976-1-yuyufen@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 11-04-19 11:53:18, Yufen Yu wrote: > This patch can avoid protential null pointer dereference for resv_map. > > As Mike Kravetz say: > Even if we can not hit this condition today, I still believe it > would be a good idea to make this type of change. It would > prevent a possible NULL dereference in case the structure of code > changes in the future. What kind of change would that be and wouldn't it require much more changes? In other words it is not really clear why is this an improvement. Random checks for NULL that cannot happen tend to be more confusing long term because people will simply blindly follow them and build a cargo cult around. > Cc: Kirill A. Shutemov > Cc: Naoya Horiguchi > Cc: Michal Hocko > Suggested-by: Mike Kravetz > Signed-off-by: Yufen Yu > --- > mm/hugetlb.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 97b1e0290c66..fe74f94e5327 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4465,6 +4465,8 @@ int hugetlb_reserve_pages(struct inode *inode, > */ > if (!vma || vma->vm_flags & VM_MAYSHARE) { > resv_map = inode_resv_map(inode); > + if (!resv_map) > + return -EACCES; > > chg = region_chg(resv_map, from, to); > > -- > 2.16.2.dirty -- Michal Hocko SUSE Labs