From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE0CC2882A9 for ; Fri, 9 Jan 2026 15:41:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767973273; cv=none; b=PTv3+r/A2kV+Jtr9TqCVbTY0qUNuvxsVufiyLl/o1Ug84926LyyNB3m3ia/5KRYuuL/u5ZXPBMzDN8iRwl4XmektFxVcvJLujWpQklKRMi3QOsZL82yTP6iv7SLcADAI8zwaV/ghxEsjledQFiCjxtZz9tJI+Nz43lYfNjUJkog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767973273; c=relaxed/simple; bh=zjirbLzk5y4/eQmZlP5l5XZ6LrVCdp2/2cmDJBEPpGE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O9wuEZwL0upRzDhkOPuU7fSjG/M72MFWc85eVFdNXCQ3R6Te/qvt0p+lvGXFi98LUGnDiCjFA8np+AIrmc12SAnYCxqkBHkJFuwDJndhOy1NRTXiWPjAomjcLyyKjYasVxJhLaUqJbJ6TcqMiK4TdzbipsLQAfQ50u/cqGeJ+eU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LJx/Awqs; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LJx/Awqs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFDDEC4CEF1; Fri, 9 Jan 2026 15:41:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767973273; bh=zjirbLzk5y4/eQmZlP5l5XZ6LrVCdp2/2cmDJBEPpGE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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