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 685E035E53D for ; Fri, 9 Jan 2026 14:18:43 +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=1767968323; cv=none; b=qYQpKr3IReHWBrWcptehxRTtkJRcjBKSfThAYixecQv9xZLmgJd3xjRE8MsCiKZq0Y4mx8u+tPKHtz2kJj0EEgSG1SiTKXR6K5r8w3zPqp8jTwx//iJqNfdTcTDCYc7oK/VuDg9CDBKO2fJ8OTyGX+nSV47LWfIowt9zaPQyaIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767968323; c=relaxed/simple; bh=UDfqyU5R4oLLX8JH9TDhDkX5WS5UHEQCcMVVXXhb5Rk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aZo/z62ja/kUg2U4xPVv0vsm3zFsHUNdWfbWm/00NUlD3s2D3wmnTWdlv+kHo47Uw04EkkTAUAUmcJMCHI7nzGho3SRRTJQ+g/j8idVeucmmn9Cx9YyG3rM/t207a6T6OMREL2q/0oFmo5iohVus3d/Ck8GOmw+FLzFL5NTxoaI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Em9yl8Wd; 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="Em9yl8Wd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BED19C4CEF1; Fri, 9 Jan 2026 14:18:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767968323; bh=UDfqyU5R4oLLX8JH9TDhDkX5WS5UHEQCcMVVXXhb5Rk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Em9yl8Wd0UCElsUBhOZ0qvCWAxk1C4K9p5Lvje1H3awjUuSqe2lvpWqlksPe+z/Li 0JkJjbM9U3Rr6t/ZaPhfVOWqZCPW5OwXQxfTWuZGb1psUVwBj+Nm/SOnXcA7vtKhwB OuQ4twfmRIWt/3kCMRvMFoW5fO3HncSuXTuFTgkXSrcVdLUJAGyfHCEVx00yi6fghr bscwS8QE4EtbRtcAj8ZuXOVM8j/u8h1EGDuKOiipdaPHO4GImJY5DYgGBqxCQg6HrX H6SjFQyUhBqcoNKm57PVRLpyOZ0IPeVVGf0VkqjpkteSERIX5DlDFmRY4POzeHZp+h vaIhRUI1CFLGA== Message-ID: Date: Fri, 9 Jan 2026 15:18:37 +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 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. -- Cheers David