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Thu, 7 May 2026 10:32:10 +0000 (GMT) Date: Thu, 7 May 2026 12:32:09 +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: <43815634-29d3-4fa4-b967-0e251ff32f73-agordeev@linux.ibm.com> References: <20260504130434.2285053-1-agordeev@linux.ibm.com> <20260507093433.q5xybwumryxclnqy@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: <20260507093433.q5xybwumryxclnqy@master> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=XPQAjwhE c=1 sm=1 tr=0 ts=69fc6a30 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=kj9zAlcOel0A:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=D19gQVrFAAAA:8 a=7CFNzQo_ZtPcNetzl2UA:9 a=CjuIK1q_8ugA:10 a=W4TVW4IDbPiebHqcZpNg:22 X-Proofpoint-ORIG-GUID: 8QOWfc7k0b7o7pCZUW67IeWT83QfImhq X-Proofpoint-GUID: qN--_Yog5Tix-ByckweoU--16gQTXerf X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA3MDEwMCBTYWx0ZWRfX2wTtXQzvHzvL xI8BnlJ8Pxm/3TvmS47XwcJZexg69P1SXrHM6Zyz/Lmif+mjbOqNI9O3UpjG6WHrx9tsMNzaTwa iVOWgkeh+TLRZO96TOmQTUGXaRJTIleMJC09wJpG+pvyIEeNo9qBC1Ir5asWJa4YNRDyJRHcb18 aEEFXQQQ8pzT32KUPHJxQ2n2tT0TFk4Ocb/WCIhT3npPMra0Qf2kC6B5WasnW8oUbcyQDTziI+z SNERrdIjFWMpS/2q2Qf+S5EyBC4hQpOX+BvTvihoSsJxdx7Y+2WJpw1GmEmr8aZlDiqpg3WzQ5t ommhqmlI//BmBSpjvaZpeCcO7SXDU6+0HhVwFbJoel/lbDwN9tb0Q1Fpfjq3OJFvK1aP/mkkOuE P5FRJRKcna2FfalADhYzlKVSwAkrN54krW7KT2emrntOZZEVu+6VClcqx1cjQ1Uyi60W56xnqOW wVIR9MK2vEYAGnNYntA== 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=2026-05-06_02,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 adultscore=0 spamscore=0 priorityscore=1501 impostorscore=0 phishscore=0 malwarescore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605070100 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. > > > > if (!pvmw->ptl) { > > spin_lock(ptl); > >-- > >2.51.0 > > > > -- > Wei Yang Thanks!