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Mon, 11 Nov 2025 07:07:54 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 7443926816316 X-SMAIL-UIID: 4FF7BC97C0A44A949683DE4B3C1BD111-20251111-070754-1 From: Hillf Danton To: Lance Yang Cc: Harry Yoo , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/1] mm/hugetlb: fix possible deadlocks in hugetlb VMA unmap paths Date: Tue, 11 Nov 2025 07:07:43 +0800 Message-ID: <20251110230745.9105-1-hdanton@sina.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 46EAC1C0004 X-Stat-Signature: 8djknp6zg75c8nmj6g9ex3msjxagywtd X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1762816078-731820 X-HE-Meta: U2FsdGVkX1/qhDltDk6UhmfSxduqVv91Ne29j9ZyVIB116IIm+8/X8/b8D2KdbhV7Qyr9rJaSHu4rEBkr5gGAeo02d7Ij+0RL6HYZASG6CyfQN3EktRRdVkT+ZNhHPzK6iwqhy2pmWfDus0FT5TbkkccQDQ7OOVC+VLgPlhVBoANea7dziVm+eQK3c3kzZDkTahr9x6kzLRAq/rV2X4K2fM/E5X2qVk6HGSwk+chGyyZSnec7o0SHQO3zuD40cpdyTRLPNlzbBxoBu8HNgL7U5TF0pHNQEj0pyPhXyNY334kmFXrdhBXCRbfzV7Kgl+u668kk5vYQX1cWTy5/xQPHyh+lrLiHTfsn/2KRzdJzTiT2JJqQfuGJ+6hSQ5sbALQry7eq7PVZkOmk2u6OC13/X75BZQi0rVEmG+Cimdt14Q4epi97fdoONtICbGCQ0OwMPsebju7QD9+wYCsghVaJB46H7So/cKzNU0RhztUSwCMtTeaQu6OSSjoB+UWfIaOKja/poz19rW12MrmDd0Xs/zHFF26MbPqRN8qQp2VsAwqSEj1iuGiCjU0YpzT0yPaCCdhYVXpCOmZqFuhiA6rmt9xuVa28NdjHqSa3x/b4LN7ediZtd1Oo5c+U4RMoyedcqcFDVOBLfyTENiWr+TSEN82Jw8JkbBHeDHjKGTd1UZdESb+c47Fi2LDj+M5b5PAAtpPXoT6K4XMxnuG4al/QwEX93EYUvJSneMZTbw+Ln+oWMVQ2BYimdG7LvhBHt6uz/PykNUnt+8d6k39w3oziCUDbA/8THsUht+XjgwhKyNkEVNw+ZWVOzb2VUHOzd4rIonZ4vkn7aBKHQWRyG0RrdIFezO+/sAl742btjMage3ewNNQc1zf90mxYIKraRg1dC+EOKUW5YeyLVK5iuCje1QviHBNW/Cwmc42w64DdyIgcqm5Y85FE26T3U7oizihwFOnQOhL/8hjitlNVQe 29RY8DgA mGN6MffQMMR5z/pkQk61tUaQ1Ov06+2KKS5Ti0E+SBqkF0rXSAbRbYVXyhpthen5I1oTqUoiTBTzpVhkfTy6rRNybsCX/56L/GHpi0JyTH+Q0Hx0FKlyuuhGWhwtFEMK83Vw5Y/aY42wKusekfRYPvvP85Oq/9za565paGKND3XZofKqGFDmVy3MTWSUrFC/NEtdmgdZaYMYy5kQty8clE7hXZlA9NMo7F1qMbWwRy5Dw8BUaSNmZ6Y2/d2KV9Ie2tUeNdfAPYDWRqSF17NGFgiLG6A== 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 Tue, 11 Nov 2025 00:39:29 +0800 Lance Yang wrote: > On 2025/11/10 20:17, Harry Yoo wrote: > > On Mon, Nov 10, 2025 at 07:15:53PM +0800, Lance Yang wrote: > >> From: Lance Yang > >> > >> The hugetlb VMA unmap path contains several potential deadlocks, as > >> reported by syzbot. These deadlocks occur in __hugetlb_zap_begin(), > >> move_hugetlb_page_tables(), and the retry path of > >> hugetlb_unmap_file_folio() (affecting remove_inode_hugepages() and > >> unmap_vmas()), where vma_lock is acquired before i_mmap_lock. This lock > >> ordering conflicts with other paths like hugetlb_fault(), which establish > >> the correct dependency as i_mmap_lock -> vma_lock. > >> > >> Possible unsafe locking scenario: > >> > >> CPU0 CPU1 > >> ---- ---- > >> lock(&vma_lock->rw_sema); > >> lock(&i_mmap_lock); > >> lock(&vma_lock->rw_sema); > >> lock(&i_mmap_lock); > >> > >> Resolve the circular dependencies reported by syzbot across multiple call > >> chains by reordering the locks in all conflicting paths to consistently > >> follow the established i_mmap_lock -> vma_lock order. > > > > But mm/rmap.c says: > >> * hugetlbfs PageHuge() take locks in this order: > >> * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) > >> * vma_lock (hugetlb specific lock for pmd_sharing) > >> * mapping->i_mmap_rwsem (also used for hugetlb pmd sharing) > >> * folio_lock > >> */ > > Thanks! You are right, I was mistaken ... > > > > > I think the commit message should explain why the locking order described > > above is incorrect (or when it became incorrect) and fix the comment? > > I think the locking order documented in mm/rmap.c (vma_lock -> i_mmap_lock) > is indeed the correct one to follow. > > This fix has it backwards then. I'll rework it to fix the actual violations. > Break a leg, better after taking a look at ffa1e7ada456 ("block: Make request_queue lockdep splats show up earlier")