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Fri, 8 May 2026 05:15:46 +0000 (GMT) Date: Fri, 8 May 2026 07:15:45 +0200 From: Alexander Gordeev To: Wei Yang Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Anshuman Khandual , Oscar Salvador , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Heiko Carstens , Vasily Gorbik Subject: Re: [PATCH v2] mm/page_vma_mapped_walk: Use ptep_get_lockless() for lockless access Message-ID: <4da2d354-808d-463e-ac85-5b1f3fd51618-agordeev@linux.ibm.com> References: <20260504130434.2285053-1-agordeev@linux.ibm.com> <20260507093433.q5xybwumryxclnqy@master> <43815634-29d3-4fa4-b967-0e251ff32f73-agordeev@linux.ibm.com> <20260508010040.o7bypjnfceeqloeq@master> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260508010040.o7bypjnfceeqloeq@master> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA4MDA0OSBTYWx0ZWRfX6XS3Cvw9NV0z xlYifDzHr3tyAeePigHppZ1FN8PzWP7QbruN2WUTtZXGOT3k/04LGDB+KiRMUYD0PdfTsUj6XuY pnnpt4CiB9m3Jb15iEmLkQCjtj4Rs4uRKQe026JSXqoPSqjmFLdMNRL05qi7NlRB3kwELSf0QbS gcCoCddrT/Y3SKtT3cF6+72NFcOabNbD0p78vaA2GAOhZ/7hUScbIiblUAiNMU2BucjM0ctvEBp S2hmEtikMAKFs2+VsXy/nPGDvlC3joq7B3o67U0dZWlmguC5I8TtU0KS3VaOzY3Nq4FF6f/2thW 8eBhjggHDElre3pbbQ5xfCi0Ei3VOInP8/yZGYVo2JDmjSJ9zN3ZVj+/jJbPr9h7b6kYu33ipQC b3SQGA9i3pmEERHGqbTTkkNjNRhK0pqM5i2PTykON6c1J+G0EfQYLWV5NrZVWEOUc32GxyHM7cj N5KQW0lX4BRs04na3dA== X-Proofpoint-GUID: XG4_XHjMB35HXTS7RQBDKeyexlMwZ0oo X-Proofpoint-ORIG-GUID: 9n5EEfaIrT16Q-gA8mKmo7rgLx7Lijzc X-Authority-Analysis: v=2.4 cv=eu/vCIpX c=1 sm=1 tr=0 ts=69fd7187 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=D19gQVrFAAAA:8 a=KSUS2Lu9pVKMSydAcJkA:9 a=CjuIK1q_8ugA:10 a=W4TVW4IDbPiebHqcZpNg:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-07_02,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 suspectscore=0 malwarescore=0 bulkscore=0 impostorscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605080049 On Fri, May 08, 2026 at 01:00:40AM +0000, Wei Yang wrote: > On Thu, May 07, 2026 at 12:32:09PM +0200, Alexander Gordeev wrote: > >On Thu, May 07, 2026 at 09:34:33AM +0000, Wei Yang wrote: > >> >@@ -310,7 +310,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > >> > goto restart; > >> > } > >> > pvmw->pte++; > >> >- } while (pte_none(ptep_get(pvmw->pte))); > >> >+ } while (pte_none(ptep_get_lockless(pvmw->pte))); > >> > >> As Oscar mentioned in lkml.org/lkml/2026/4/27/630, map_pte() may take the > >> lock. So probably it is not right? > > > >If I read the code correctly map_pte() might take the lock, but also > >might not take it. If it took the lock and uses ptep_get_lockless(), > >then it is fine. But if it did not take the lock and uses ptep_get(), > >then it is an issue. > > > > So the rule here is: > > * ptep_get_lockless() could be used for locked and not locked > * ptep_get() only used when locked > > Right? Yes, this is my assumption. > >> > > >> > if (!pvmw->ptl) { > >> > spin_lock(ptl); > >> >-- > >> >2.51.0 > >> > > >> > >> -- > >> Wei Yang > > > >Thanks! > > -- > Wei Yang > Help you, Help me