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t=1767965955; bh=1dPK506i2U9+WjR9nExbFYZAgBn/2wtpSi+tYqMsfpU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tfOOTzSR0lNSJxCRfGRDE6qkkN79kEa+28zbT7JNP9L9D+DfDzq3leP+uyflJww/n a6nFO5vo65KQk30H0/sUTgm1dd9xIFSFOWwp1TIvdvoNGAAEwAIeeTMzDm+FTT6Vkp QWovGhbbmg6LpiSFQuXAuEpva4aESEQ8CCPG9jnr09Nl5fEOHPTULOMC8wUJtBZPzb Ie6aRjxkVC+gP0fELUkHSx8UJIcBk92oBnOjQIpQ9OWBiDO35mDVAjln+6hP7Iq0A5 0vamyVvetJJeeWnHLdeGmpLJec19ygROhxOak9cvvTO8QgQUGBB2PXIVGfvLgMzq15 kCtR1JQDNWO2g== Message-ID: <920c641e-e092-46f0-89cb-0f1c130d979a@kernel.org> Date: Fri, 9 Jan 2026 14:39:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: fix hugetlbfs deadlock by respecting lock ordering To: Jinchao Wang , Matthew Wilcox , Andrew Morton , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com References: <20260109034723.1342798-1-wangjinchao600@gmail.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6AEA914000E X-Stat-Signature: b1ioh7p1kwnac8be5gxuknae3i4t1pni X-Rspam-User: X-HE-Tag: 1767965956-918757 X-HE-Meta: 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 tyuAQs+8 JK3bJTVnJuqaeMCZfVaF7VppWm7BSWh90TweV/izn817DHMuubwUO1DBi8TtuzspuWmSCrgcMYOKlUL3VKoGjpe+0+XncCgA/CEo2YT2Q0jFsfzuH239ZZv7jjjPA2wlJbUJX7v/NlSihyGb/LTO/JRHawTBzCxPVhie01hnxsy0UdHjmAEf0kNIweRytT/8OiZ96PCpSMHJW4+qADb54+hnzqo8Og8Gu8J1WD1cM27G+apj2gGilEfSvpBc1vxrUhpqw4KvJzOfBVu2PG36yhm4oJ71b7Q6k5RpK1ddfuc7G1PJDQru+qtSL3WR4/JQZzaO0NyTI+p7/wOtM8dFfdr8tniUCN/5kuX8TPrUcCoW5FMk= 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 1/9/26 04:47, Jinchao Wang wrote: > Fix an AB-BA deadlock between hugetlbfs_punch_hole() and page migration. > > The deadlock occurs because migration violates the lock ordering defined > in mm/rmap.c for hugetlbfs: > > * hugetlbfs PageHuge() take locks in this order: > * hugetlb_fault_mutex > * vma_lock > * mapping->i_mmap_rwsem > * folio_lock > > The following trace illustrates the inversion: > > Task A (punch_hole): Task B (migration): > -------------------- ------------------- > 1. i_mmap_lock_write(mapping) 1. folio_lock(folio) > 2. folio_lock(folio) 2. i_mmap_lock_read(mapping) > (blocks waiting for B) (blocks waiting for A) > > Task A is blocked in the punch-hole path: > hugetlbfs_fallocate > hugetlbfs_punch_hole > hugetlbfs_zero_partial_page > folio_lock > > Task B is blocked in the migration path: > migrate_pages > unmap_and_move_huge_page > remove_migration_ptes > __rmap_walk_file > i_mmap_lock_read > > To fix this, adjust unmap_and_move_huge_page() to respect the established > hierarchy. If i_mmap_rwsem is acquired during try_to_migrate(), hold it I'm confused. Isn't it unmap_and_move_huge_page() that grabs the i_mmap_rwsem during hugetlb_page_mapping_lock_write() (where we do a try-lock)? We now handle file-backed folios correctly I think. Could we somehow also be in trouble for anon folios? Because there, we'd still take the rmap lock after grabbing the folio lock. -- Cheers David