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 181E719DFB3; Tue, 16 Jul 2024 15:51:14 +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=1721145074; cv=none; b=go/bfzWTR07QPrBDqDHWDcs0eW33Rl+6cn6UUdj2enTNHSqNgRle6qpzBpR68HjP//mJ5c4cy6uTD0suxe1BBW0PYYjAmid8g+C0pC5gz3FFIGF8zH2q1PCXDyUbUaHa+bgYBnazHtAqYVRtGc08b4bxVQWQ5EBM7W2OzTJNGd8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721145074; c=relaxed/simple; bh=P8yUMUdYJo5yQzSVmJJyj0B29X2igIf6xMOifHR9P4o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Qeom1IeEDnuFcX7bKOu8c5qZoos/GN3lNQ1ypjmiJCdKqFu5SeuZ5gyawCtQ1Gsp+v34BNp8pGsSwFbgfoqO45RasDSSIUBnpko8BYXzhwfkmuEVJJiiKJOOsvvBNLWZfUiTq640TjB/H7F1G/9gSeDxWtIO8FFrERDjflJBivM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fghS3DVh; 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="fghS3DVh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64DFDC4AF0D; Tue, 16 Jul 2024 15:51:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1721145074; bh=P8yUMUdYJo5yQzSVmJJyj0B29X2igIf6xMOifHR9P4o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fghS3DVhmZ7ETg9it9vyZEraAvM7jznKIe/OAGtvlP/2YIxHa0YRlTh0UbsbJy1t1 NziY44xjQEC4tyRI+sdEZAPZyoxbwr5dK29soElsotRincEmJ9zxgLlQhRB2DIPakc bhWLP1FlWGNYjIROaxTu23VvEzyW7zUBbNtFNMps= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Hugh Dickins , Baolin Wang , Barry Song , David Hildenbrand , Kefeng Wang , "Matthew Wilcox (Oracle)" , Nhat Pham , Yang Shi , Zi Yan , Andrew Morton Subject: [PATCH 6.9 088/143] mm: fix crashes from deferred split racing folio migration Date: Tue, 16 Jul 2024 17:31:24 +0200 Message-ID: <20240716152759.360945987@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240716152755.980289992@linuxfoundation.org> References: <20240716152755.980289992@linuxfoundation.org> User-Agent: quilt/0.67 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 6.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins commit be9581ea8c058d81154251cb0695987098996cad upstream. 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 Signed-off-by: Greg Kroah-Hartman --- mm/memcontrol.c | 11 ----------- mm/migrate.c | 13 +++++++++++++ 2 files changed, 13 insertions(+), 11 deletions(-) --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7609,17 +7609,6 @@ 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 +++ b/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.