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Wed, 5 Jul 2023 14:48:26 GMT Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7B22A5805A; Wed, 5 Jul 2023 14:48:26 +0000 (GMT) Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B182B58051; Wed, 5 Jul 2023 14:48:14 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.43.47.143]) by smtpav02.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 5 Jul 2023 14:48:14 +0000 (GMT) X-Mailer: emacs 29.0.91 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Hugh Dickins , Andrew Morton Cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 04/31] mm/pgtable: allow pte_offset_map[_lock]() to fail In-Reply-To: <8218ffdc-8be-54e5-0a8-83f5542af283@google.com> References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> <8218ffdc-8be-54e5-0a8-83f5542af283@google.com> Date: Wed, 05 Jul 2023 20:18:12 +0530 Message-ID: <87y1juxvmb.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-GUID: GDmSVGrS8syCV2n7TgQ4YZtWM0lquLyc X-Proofpoint-ORIG-GUID: 4X2trLtTkHXz7Z42SusOeEbcViwHSz6O X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-07-05_06,2023-07-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 clxscore=1011 impostorscore=0 priorityscore=1501 mlxscore=0 spamscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 mlxlogscore=949 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2307050131 X-Rspamd-Queue-Id: B2C5D180003 X-Rspam-User: X-Stat-Signature: mt8urpqjafftj4gnbqogw5nihhx83naw X-Rspamd-Server: rspam01 X-HE-Tag: 1688568557-272745 X-HE-Meta: U2FsdGVkX1864M4rp6Ffe9lUlW2GHjES4FBMZH1DJJYFWMwGhZkWHSMH0ykeCYE+1qGZwO4OYZ4c541a0ps92NJ8WOItlpo4p9/A24KlDNfZSUNg5JapNQOVAPS96lF48zuHzvElmxpYaHEU1d1ty7tCXkqryE3J0TwGg0CJHfVyMgKAf+b0k4zjbGo8yMg/kGKdp6CssCzgtQZWTR7tqdOZrvjRb6laCSRo53bLPgxYnBYJ88Q1h0G9JVQofHOBp0NAGYTS3pU7XSdEGMHfhLbremQ40wIp4uTbdHYcRoT3O42JhBV9rwSOmeyn7ReXjnSJOWDNNU0EwwADHN7/rN98AXC1EU7GRmTA8XGyGmreEIu1+Ch1Q+tEqNgR0y7AxRpQRdzBkgV0v7IU11nw86YBKHotzOEwsz5+XQeIbUhFQaomp2DuyWz0JuvjAbyHnr5PGgNuuUyu4uPYJSr3ucDwiy9MCOOhuQWzUgiKVVsPAmAhLrhziq1UF9LC3iCanNu6yo32hp/se/mEhCGZbNvwTupPYR7qa7AOvSag5ch7U+VqbBIYlvMAhXy05M8u2wJWHZgrkHzrTGQWilcRqb0IVtX4pYhE6BGcwZ4Rs9ez7FVPrnpw7UzD1dyMYB0PLX/gaGh2zQWPeebVbEQC0ZN2su03+LB+bNJiGYD5vKRWJHD8PF6Fl0k/R9l36P30ylbyNt1S23XREDfLz5DeXAsU615zEZlOGsOTOC3WkfJhAN07UQc4sQFW3vf3RuldtMd7VGLmBT+/KgJEFgiBlVhl392B2JmcOALyAcE5nqhvM7kKufSqAro+Q3G6idhgNK+MhWyPidsFEW5h/FAr6in8LWfYpODjyFytE0Z/BqC6CU/NNOs0vLtgusSgHLe/wFkaTK5gArd3GA5g75ORXlAnObs7ls8FBmPnCbc7QFRqXqMSAbI6qrF60KFlfs47Cg/Kzl40ZViwJvTljm6 Oh3SeVws HeasOyizLnebglxmyXWXO56f1qg2J8wmedYZUW7/asA8sYQmUAj29/dTuPcWBhp4Rv+aO3SeyCvrQdLgMVpdzDw3Mg0rsMO4IVfV82DQJl0Cc/OVT8w7ZQwLKTYZ/xJD4pJ3QRIGX8DZsbatzK9HWKanl9w== 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: Hi Hugh, Sorry for not checking about this before. I am looking at a kernel crash (BUG_ON()) on ppc64 with 4K page size. The reason we hit BUG_ON() is beause we have pmd_same calling BUG_ON on 4K with hash translation. We don't support THP with 4k page size and hash translation. Hugh Dickins writes: .... + > +pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, spinlock_t **ptlp) > +{ > + pmd_t pmdval; > + pte_t *pte; > + > + pte = __pte_offset_map(pmd, addr, &pmdval); > + if (likely(pte)) > + *ptlp = pte_lockptr(mm, &pmdval); > + return pte; > +} > + > +pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, spinlock_t **ptlp) > +{ > + spinlock_t *ptl; > + pmd_t pmdval; > + pte_t *pte; > +again: > + pte = __pte_offset_map(pmd, addr, &pmdval); > + if (unlikely(!pte)) > + return pte; > + ptl = pte_lockptr(mm, &pmdval); > + spin_lock(ptl); > + if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) { > + *ptlp = ptl; > + return pte; > + } > + pte_unmap_unlock(pte, ptl); > + goto again; > +} What is expected by that pmd_same check? We are holding pte lock and not pmd lock. So contents of pmd can change. -aneesh