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 B220946B5; Wed, 3 Jul 2024 02:12:44 +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=1719972764; cv=none; b=rYzNV5dOT0J/cYZO5I9leVTXnGLj9dQ4yLzbOv/y0sg2EDK9/GmB8qLrpQY0fj1bhVzEhl9u/QWcVNB+JLg+ukB94G1hxjcQTrCEQ2kjccZt8rJzhFgoiCKrYt8fmv6zEcwPkfVcY2w8mCBVaxUMEWnoaIeF6NHfXjgd+K7sJP0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719972764; c=relaxed/simple; bh=WMOGJM/eIvbSlzNXfRxZCrAPHE9Qou+Pouy5o1n7a5M=; h=Date:To:From:Subject:Message-Id; b=N11r8CIsnDaVKYp2bM8dDOAUpeSZEhE3++AMaLPHeZ00D3EN3n9Ps0h7T9s7QquCo0cFTvnM0DLGL+8+22NUda4PYhA6QVQpkLBV0U9UMVFElU/zrL93SdBV8jrhA2BFqdmedrQpEfXB70F0tzRSNlfFzYE9aoTFIFxKaCI/6b0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=fYq6RcCN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="fYq6RcCN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 394BFC116B1; Wed, 3 Jul 2024 02:12:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1719972764; bh=WMOGJM/eIvbSlzNXfRxZCrAPHE9Qou+Pouy5o1n7a5M=; h=Date:To:From:Subject:From; b=fYq6RcCNfTEIneJMUHvHnUFOSobHgMUcuejTgfkF1pRW+aho2luCrFgQiSU4Ndr5A ahAl/o64XIVY4yplTkKvBZgxkH4KZymXJ93Y5l80BjzT6COqbb+tkvRZeakR+bTMKK ZBkHISuyq8v4GfQ9IAMCQIek1oUVXr5qqElZ6XQs= Date: Tue, 02 Jul 2024 19:12:43 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,willy@infradead.org,wangkefeng.wang@huawei.com,stable@vger.kernel.org,shy828301@gmail.com,nphamcs@gmail.com,david@redhat.com,baolin.wang@linux.alibaba.com,baohua@kernel.org,hughd@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-fix-crashes-from-deferred-split-racing-folio-migration.patch added to mm-hotfixes-unstable branch Message-Id: <20240703021244.394BFC116B1@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: fix crashes from deferred split racing folio migration has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-fix-crashes-from-deferred-split-racing-folio-migration.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-crashes-from-deferred-split-racing-folio-migration.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Hugh Dickins Subject: mm: fix crashes from deferred split racing folio migration Date: Tue, 2 Jul 2024 00:40:55 -0700 (PDT) Even on 6.10-rc6, I've been seeing elusive "Bad page state"s (often on flags when freeing, yet the flags shown are not bad: PG_locked had been set and cleared??), and VM_BUG_ON_PAGE(page_ref_count(page) == 0)s from deferred_split_scan()'s folio_put(), and a variety of other BUG and WARN symptoms implying double free by deferred split and large folio migration. 6.7 commit 9bcef5973e31 ("mm: memcg: fix split queue list crash when large folio migration") was right to fix the memcg-dependent locking broken in 85ce2c517ade ("memcontrol: only transfer the memcg data for migration"), but missed a subtlety of deferred_split_scan(): it moves folios to its own local list to work on them without split_queue_lock, during which time folio->_deferred_list is not empty, but even the "right" lock does nothing to secure the folio and the list it is on. Fortunately, deferred_split_scan() is careful to use folio_try_get(): so folio_migrate_mapping() can avoid the race by folio_undo_large_rmappable() while the old folio's reference count is temporarily frozen to 0 - adding such a freeze in the !mapping case too (originally, folio lock and unmapping and no swap cache left an anon folio unreachable, so no freezing was needed there: but the deferred split queue offers a way to reach it). Link: https://lkml.kernel.org/r/29c83d1a-11ca-b6c9-f92e-6ccb322af510@google.com Fixes: 9bcef5973e31 ("mm: memcg: fix split queue list crash when large folio migration") Signed-off-by: Hugh Dickins Reviewed-by: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Hugh Dickins Cc: Kefeng Wang Cc: Matthew Wilcox (Oracle) Cc: Nhat Pham Cc: Yang Shi Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- mm/memcontrol.c | 11 ----------- mm/migrate.c | 13 +++++++++++++ 2 files changed, 13 insertions(+), 11 deletions(-) --- a/mm/memcontrol.c~mm-fix-crashes-from-deferred-split-racing-folio-migration +++ a/mm/memcontrol.c @@ -7823,17 +7823,6 @@ void mem_cgroup_migrate(struct folio *ol /* Transfer the charge and the css ref */ commit_charge(new, memcg); - /* - * If the old folio is a large folio and is in the split queue, it needs - * to be removed from the split queue now, in case getting an incorrect - * split queue in destroy_large_folio() after the memcg of the old folio - * is cleared. - * - * In addition, the old folio is about to be freed after migration, so - * removing from the split queue a bit earlier seems reasonable. - */ - if (folio_test_large(old) && folio_test_large_rmappable(old)) - folio_undo_large_rmappable(old); old->memcg_data = 0; } --- a/mm/migrate.c~mm-fix-crashes-from-deferred-split-racing-folio-migration +++ a/mm/migrate.c @@ -415,6 +415,15 @@ int folio_migrate_mapping(struct address if (folio_ref_count(folio) != expected_count) return -EAGAIN; + /* Take off deferred split queue while frozen and memcg set */ + if (folio_test_large(folio) && + folio_test_large_rmappable(folio)) { + if (!folio_ref_freeze(folio, expected_count)) + return -EAGAIN; + folio_undo_large_rmappable(folio); + folio_ref_unfreeze(folio, expected_count); + } + /* No turning back from here */ newfolio->index = folio->index; newfolio->mapping = folio->mapping; @@ -433,6 +442,10 @@ int folio_migrate_mapping(struct address return -EAGAIN; } + /* Take off deferred split queue while frozen and memcg set */ + if (folio_test_large(folio) && folio_test_large_rmappable(folio)) + folio_undo_large_rmappable(folio); + /* * Now we know that no one else is looking at the folio: * no turning back from here. _ Patches currently in -mm which might be from hughd@google.com are mm-fix-crashes-from-deferred-split-racing-folio-migration.patch