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Wed, 19 Feb 2020 03:49:04 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 01J3lvE8149521; Wed, 19 Feb 2020 03:49:04 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 2y8ud25fr9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 19 Feb 2020 03:49:04 +0000 Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 01J3n2cC005269; Wed, 19 Feb 2020 03:49:02 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 18 Feb 2020 19:49:02 -0800 Subject: Re: [PATCH] mm/hugetlb: avoid get wrong ptep caused by race To: "Longpeng (Mike)" , Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, arei.gonglei@huawei.com, weidong.huang@huawei.com, weifuqiang@huawei.com, kvm@vger.kernel.org References: <1582027825-112728-1-git-send-email-longpeng2@huawei.com> <20200218205239.GE24185@bombadil.infradead.org> <593d82a3-1d1e-d8f2-6b90-137f10441522@huawei.com> From: Mike Kravetz Message-ID: <8292299c-4c5a-a8cb-22e2-d5c9051f122a@oracle.com> Date: Tue, 18 Feb 2020 19:49:01 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <593d82a3-1d1e-d8f2-6b90-137f10441522@huawei.com> Content-Type: text/plain; charset=gbk Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9535 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 spamscore=0 suspectscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002190026 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9535 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 bulkscore=0 spamscore=0 priorityscore=1501 phishscore=0 impostorscore=0 mlxlogscore=999 clxscore=1015 adultscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002190026 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000011, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2/18/20 6:09 PM, Longpeng (Mike) wrote: > =D4=DA 2020/2/19 4:52, Matthew Wilcox =D0=B4=B5=C0: >> On Tue, Feb 18, 2020 at 08:10:25PM +0800, Longpeng(Mike) wrote: >>> { >>> - pgd_t *pgd; >>> - p4d_t *p4d; >>> - pud_t *pud; >>> - pmd_t *pmd; >>> + pgd_t *pgdp; >>> + p4d_t *p4dp; >>> + pud_t *pudp, pud; >>> + pmd_t *pmdp, pmd; >> >> Renaming the variables as part of a fix is a really bad idea. It obsc= ures >> the actual fix and makes everybody's life harder. Plus, it's not even >> renaming to follow the normal convention -- there are only two places >> (migrate.c and gup.c) which follow this pattern in mm/ while there are >> 33 that do not. >> > Good suggestion, I've never noticed this, thanks. > By the way, could you give an example if we use this way to fix the bug= ? Matthew and others may have better suggestions for naming. However, I wo= uld keep the existing names and add: pud_t pud_entry; pmd_t pmd_entry; Then the *_entry variables are the target of the READ_ONCE() pud_entry =3D READ_ONCE(*pud); if (sz !=3D PUD_SIZE && pud_none(pud_entry)) ... ... pmd_entry =3D READ_ONCE(*pmd); if (sz !=3D PMD_SIZE && pmd_none(pmd_entry)) ... ... BTW, thank you for finding this issue! --=20 Mike Kravetz