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b=LJx/Awqs0W8dnmRGPKis4lRGYO1YtKIv2LCgMk3hfDNR1EFX3sXp6duz0kcaTGMky H76mUFClbAmZdOaQd3ccOYADKsFcIeqkB6jX0X1GRj0JmAr9WlOQHL5UzFnAueaD/S XolUvioNXor2OXyarOz0L8T2YbvP0TrU1XhrAMWQMZtUKDqsGOfNo4sg96KSUTnBRA X6NuW57vsAdLtnbDPvjdhvU4oTXRFF8saqcL+cYLk7A6KYBwDRptIvyY3es+8suu40 S7bl8DlcxqDipdPTzcUFD5q4VC/PHQxd5Eq47chTB+ju6df/v7RiRWzHZKIrJ5EQAu Y2DuG/oHLU9tQ== Message-ID: Date: Fri, 9 Jan 2026 16:41:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: fix hugetlbfs deadlock by respecting lock ordering To: Jinchao Wang Cc: 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, syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com References: <20260109034723.1342798-1-wangjinchao600@gmail.com> <920c641e-e092-46f0-89cb-0f1c130d979a@kernel.org> 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: rspam11 X-Rspamd-Queue-Id: 76DDAC0013 X-Rspam-User: X-Stat-Signature: 47kfx3fypouk6e7nwcuc8qj6k89ubenr X-HE-Tag: 1767973274-414663 X-HE-Meta: U2FsdGVkX18AOSwBStz3CuSrL2OzSkeVfXS7jFPlLLNPoLqPMXrSmoiTcHo7x43vK9olrgT+HWUdgQH/O55cHpEYU2MfJRni0rL7/LPQ1mM/JnhWEph25W3/d3VlKNGZhxezgUMD/U4R02ZC8CfoESOt9GAz8G4LFj7jMG7c0gYK4YKtIvLYHgflRDtR/e2bb4PG1yJSIWxy56UC3FjjgjU7E4sTs4PJslU9FhXEA+8llYIIyJiF3MpBk9Zth1Wb9u+afz+Gv+BbNM0YIBiwO2lEfPK/ZNDx2HZzsKzAQIzBQTS9ve4ha+L98DRUr5hhnDEpmIfOWkHjV3/G3zRhTuqND8jqUT5a+vm/kNeBVeZksn5g3f+xajD4oV+YFqhUMAiydbRgBqaqvINJ9zrzDnH/yyn7ok2koYOau2EVSVAP1Nci7pI9TaAJHAH7vW5sYszTAJrRZVNHci16Wq6at69SpcNE+SRWoiIAoNLSEfwGxcjVIPA4rGrgpNJTVly4qqZWMFydQaSqhiNwIEaAo6yyFlCT3xgXMHysA9yPU/XrKknz/TIEsY+VPUmhrs9S035DzCLBD6Ia0dvqzY9ghCFkrDS/DsJohnlrFzSJwcOUDNsJweAmN3n42UlG2QQ1AJo6LJBDKUVvlZvNTIfpNIF4CM7Vwc3NlusMgJjMmF4g+ci0pBhIt8TirUZoO9gPo1htvPYKNceBlGoO7VMiwSOt0A414Volhl35yz5SofZ1dDQFpgp7ud0HFGJpWxVmwgmpU9MntoEyj/DWC/4knIg/XF/fe5tEx/COI1L/phcJ39Mu67JDH5jMc4WwgaW9OjmCacY6cXrtWgefaITyeysuY5CXplvqEL9GeLtX4SibGinc5RAV2jsTedeE6ATtJO/w0A3vAQJ8ohRLaRuCP+DFZhz6UhR+SD0kXnF+1B5WOCrQ3flAJJwQcQ48qEka/oLwZ9AIfTNSexmAAOw 1Kpo4f3L 9NPOP+asMdSflZ9BlsY3BRHHRGUb8RnaeflISFHYNQc0tPicjVlldeGqCkbgu6sIN+YwAVQWfdvPcXIwXudMkOL3ui4ixWaa3Wj7GpHAEHFhb9Rwtg5Pzg9tCBmYh9c7CHqvJjrORHikrC8vNWEVXVeNL1K1/tj1oeAkX40XFBqD+0u4g4AxxeeiKyagxm0XbqIQBHh616sxJajiAMv3CiE+u1YdPDw0cTWvNbnN23Ef73egCWPJZlV0D4T/Hss2Jsa3MojGuvgzQ9fw9W71HINQ27CvmQ8mcoP+/lDW/N+ufsu1xJ1vKqyui/uSGeCMjdfd2w1ZSLHHFmKggl5rzb9HBHWWHoxsIib568jSYKbQ24/V0OKHShKs62iMO6HTvPrbQaV2BtlwhHL/jib7CX6KSOI0A5mFcbhD0GCX6eV6uhs4ZywxoF8Hu/g== 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 16:32, Jinchao Wang wrote: > On Fri, Jan 09, 2026 at 03:18:37PM +0100, David Hildenbrand (Red Hat) wrote: >> On 1/9/26 15:16, Jinchao Wang wrote: >>> On Fri, Jan 09, 2026 at 02:39:08PM +0100, David Hildenbrand (Red Hat) wrote: >>>> 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)? >>> Yes, but the lock is released before remove_migration_ptes(). >>> >>> Task A can enter the race window between >>> i_mmap_unlock_write(mapping) >>> and >>> remove_migration_ptes() -> i_mmap_lock_read(mapping). >>> >>> This window was introduced by the change below: >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/mm/migrate.c?id=336bf30eb765 >> >> try_to_migrate() is not the problem, but remove_migration_ptes() ? >> >> Anyhow, I saw that Willy sent out a version. > Thank you for letting me know. For reference: https://lkml.kernel.org/r/20260109041345.3863089-1-willy@infradead.org -- Cheers David