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 B5F8A2E8DFE for ; Fri, 9 Jan 2026 13:39:15 +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=1767965955; cv=none; b=MW9C8XTGjXBjiRWv4haKCYGnaJKVu05lcQPkLbXAIweO/b0fkZgcDlCHWu6JvN14+pUxjD0AGyd1jysD2dYxxI7NXxmdpVs7H1f83ymzeLS4ItNx5b81BmChNeGOYj++Nwl9z4acAihYNzpnbbH9PcJdDF11f0NwPXqWH1hklpY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767965955; c=relaxed/simple; bh=1dPK506i2U9+WjR9nExbFYZAgBn/2wtpSi+tYqMsfpU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WLoCm0F9xG1Sp3z8jFb5PwmOUT6Qck6Pkl3dhXE4jbe7HMWDo8A23l5FsL9YAYvJGF07PUDu+NvKIPxC9v1qcpInK9ns+4iU9XIb8uXf9wDeTW49/AByB4hwfci4UBasyC0epqpqRJR0ga1x3x+pTl6KlAyMyWB7fujgq81H16w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tfOOTzSR; 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="tfOOTzSR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10482C16AAE; Fri, 9 Jan 2026 13:39:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; 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 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 , 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 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