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 9AA63146D53; Wed, 28 Jan 2026 15:58:51 +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=1769615931; cv=none; b=DVlcZfm3wqF/+D2R+MCorvkp8UBaZ6cC5fInjfPQPON2qudzfbicNEaKnN/NgB+DOW439M/GfeNSHaHWeZEBXW3zjv3TPa2whvR2bya61F9FziYY/svEd4Dq6WQyQy3O1LfBAtP55jGnDtuar2jzeAhaa7vAl/kSjoKd3fEvOhw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769615931; c=relaxed/simple; bh=FHjPgjWB4rtkBGNtuAIHjZdKnT69EzI0u+N+H9TdNxg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VVAy3zN0Kj+0f5TIcFMDaHtBDL0kPpY1fpBTgtgFic1aFlmF0hJXP9gGwjd6KaWQJu5H5Z6GrU8l5gEx3D8YeKUwU3KrGPWKyu50yWdNCYl4ItWK91yOYAKk+Gp/K/nnN6kJlgAZ/MNm1smLPAJ2oQ7PqO1R3z8SwWoZ2+9aD6I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fHnuWexQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="fHnuWexQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7DD21C4CEF1; Wed, 28 Jan 2026 15:58:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769615931; bh=FHjPgjWB4rtkBGNtuAIHjZdKnT69EzI0u+N+H9TdNxg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fHnuWexQjUcza4ZJTohYNtt+GgElxy1bV1GMk1PTSglFJmmnvgq/ND+L8ZQ0AvA+A W+vVhunrcu0stsrNWFrRrOXQ5MxRKpVskLDtPhjnDXgjnOATiSAguK+ladpe+i+6zQ tmO7v/Iw8U0JxTsSrvOZ4cGT6YOKCMVuaBssIxHQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Matthew Wilcox (Oracle)" , syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com, "David Hildenbrand (Red Hat)" , Zi Yan , Alistair Popple , Byungchul Park , Gregory Price , Jann Horn , Joshua Hahn , Liam Howlett , Lorenzo Stoakes , Matthew Brost , Rakie Kim , Rik van Riel , Vlastimil Babka , Ying Huang , Andrew Morton , Lance Yang Subject: [PATCH 6.18 156/227] migrate: correct lock ordering for hugetlb file folios Date: Wed, 28 Jan 2026 16:23:21 +0100 Message-ID: <20260128145350.067006727@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260128145344.331957407@linuxfoundation.org> References: <20260128145344.331957407@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Matthew Wilcox (Oracle) commit b7880cb166ab62c2409046b2347261abf701530e upstream. Syzbot has found a deadlock (analyzed by Lance Yang): 1) Task (5749): Holds folio_lock, then tries to acquire i_mmap_rwsem(read lock). 2) Task (5754): Holds i_mmap_rwsem(write lock), then tries to acquire folio_lock. migrate_pages() -> migrate_hugetlbs() -> unmap_and_move_huge_page() <- Takes folio_lock! -> remove_migration_ptes() -> __rmap_walk_file() -> i_mmap_lock_read() <- Waits for i_mmap_rwsem(read lock)! hugetlbfs_fallocate() -> hugetlbfs_punch_hole() <- Takes i_mmap_rwsem(write lock)! -> hugetlbfs_zero_partial_page() -> filemap_lock_hugetlb_folio() -> filemap_lock_folio() -> __filemap_get_folio <- Waits for folio_lock! The migration path is the one taking locks in the wrong order according to the documentation at the top of mm/rmap.c. So expand the scope of the existing i_mmap_lock to cover the calls to remove_migration_ptes() too. This is (mostly) how it used to be after commit c0d0381ade79. That was removed by 336bf30eb765 for both file & anon hugetlb pages when it should only have been removed for anon hugetlb pages. Link: https://lkml.kernel.org/r/20260109041345.3863089-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Fixes: 336bf30eb765 ("hugetlbfs: fix anon huge page migration race") Reported-by: syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/68e9715a.050a0220.1186a4.000d.GAE@google.com Debugged-by: Lance Yang Acked-by: David Hildenbrand (Red Hat) Acked-by: Zi Yan Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: Jann Horn Cc: Joshua Hahn Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Brost Cc: Rakie Kim Cc: Rik van Riel Cc: Vlastimil Babka Cc: Ying Huang Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/migrate.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1450,6 +1450,7 @@ static int unmap_and_move_huge_page(new_ int page_was_mapped = 0; struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; + enum ttu_flags ttu = 0; if (folio_ref_count(src) == 1) { /* page was freed from under us. So we are done. */ @@ -1490,8 +1491,6 @@ static int unmap_and_move_huge_page(new_ goto put_anon; if (folio_mapped(src)) { - enum ttu_flags ttu = 0; - if (!folio_test_anon(src)) { /* * In shared mappings, try_to_unmap could potentially @@ -1508,16 +1507,17 @@ static int unmap_and_move_huge_page(new_ try_to_migrate(src, ttu); page_was_mapped = 1; - - if (ttu & TTU_RMAP_LOCKED) - i_mmap_unlock_write(mapping); } if (!folio_mapped(src)) rc = move_to_new_folio(dst, src, mode); if (page_was_mapped) - remove_migration_ptes(src, !rc ? dst : src, 0); + remove_migration_ptes(src, !rc ? dst : src, + ttu ? RMP_LOCKED : 0); + + if (ttu & TTU_RMAP_LOCKED) + i_mmap_unlock_write(mapping); unlock_put_anon: folio_unlock(dst);