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b=YE6mao69+d5ovBJsv3rT6xknjnHv2puGnxvF+fx/B4wStdLn6guPhRx2BJgH6PzPBx34R2SnDyoeX7MbS6EJvfz7uXgKH0FjbgU/+pvaCrbFwjm14dsLiZp8q8YIyPZtJ8HsoOQ5CKDPD45KSuW3TKhusss4fYJSiVh56pO5MLQ= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033068173054;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0WBLNct._1721986727; Received: from 30.97.56.64(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WBLNct._1721986727) by smtp.aliyun-inc.com; Fri, 26 Jul 2024 17:38:47 +0800 Message-ID: <4439d559-5acf-4688-a1ad-7626bf027027@linux.alibaba.com> Date: Fri, 26 Jul 2024 17:38:47 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] mm/hugetlb: fix hugetlb vs. core-mm PT locking To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Xu , Oscar Salvador , stable@vger.kernel.org References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-3-david@redhat.com> <0067dfe6-b9a6-4e98-9eef-7219299bfe58@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: dnij9aef3dsrdxwaat65fb4yijz8p8wu X-Rspamd-Queue-Id: C61CF1A000B X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1721986731-731663 X-HE-Meta: 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 vgYK5Ugp +m4M7B80K4KR2wo20ibOKL/ib8K0OiuLHT8hp76MBzo5TnXVJdQN40y3k4Em9K4ehY5OCZyTkslwt4ZT6f/jNuwqnKdipQalDpMf7HHdS1f1zyTRURzqtFwZHBdnPo3Gvp6q4ZXh/EAWVPsU8aqHOXeIXLmf+odAJ5GMVGiuXZGO3kX+d5AC9DcPRJ0dhnOxQde0PsBcBpejKW6ye1PArLOSrUDeRvHPy6W/a 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: List-Subscribe: List-Unsubscribe: On 2024/7/26 16:04, David Hildenbrand wrote: > On 26.07.24 04:33, Baolin Wang wrote: >> >> >> On 2024/7/26 02:39, David Hildenbrand wrote: >>> We recently made GUP's common page table walking code to also walk >>> hugetlb VMAs without most hugetlb special-casing, preparing for the >>> future of having less hugetlb-specific page table walking code in the >>> codebase. Turns out that we missed one page table locking detail: page >>> table locking for hugetlb folios that are not mapped using a single >>> PMD/PUD. >>> >>> Assume we have hugetlb folio that spans multiple PTEs (e.g., 64 KiB >>> hugetlb folios on arm64 with 4 KiB base page size). GUP, as it walks the >>> page tables, will perform a pte_offset_map_lock() to grab the PTE table >>> lock. >>> >>> However, hugetlb that concurrently modifies these page tables would >>> actually grab the mm->page_table_lock: with USE_SPLIT_PTE_PTLOCKS, the >>> locks would differ. Something similar can happen right now with hugetlb >>> folios that span multiple PMDs when USE_SPLIT_PMD_PTLOCKS. >>> >>> Let's make huge_pte_lockptr() effectively uses the same PT locks as any >>> core-mm page table walker would. >> >> Thanks for raising the issue again. I remember fixing this issue 2 years >> ago in commit fac35ba763ed ("mm/hugetlb: fix races when looking up a >> CONT-PTE/PMD size hugetlb page"), but it seems to be broken again. >> > > Ah, right! We fixed it by rerouting to hugetlb code that we then removed :D > > Did we have a reproducer back then that would make my live easier? I don't have any reproducers right now. I remember I added some ugly hack code (adding delay() etc.) in kernel to analyze this issue, and not easy to reproduce. :(