From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755042AbaCaASu (ORCPT ); Sun, 30 Mar 2014 20:18:50 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36359 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752991AbaC3XZB (ORCPT ); Sun, 30 Mar 2014 19:25:01 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Weijie Yang" , "Krzysztof Kozlowski" , "Hugh Dickins" , "Linus Torvalds" Date: Mon, 31 Mar 2014 00:23:35 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 089/200] mm/swap: fix race on swap_info reuse between swapoff and swapon In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.56-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Weijie Yang commit f893ab41e4dae2fe8991faf5d86d029068d1ef3a upstream. swapoff clear swap_info's SWP_USED flag prematurely and free its resources after that. A concurrent swapon will reuse this swap_info while its previous resources are not cleared completely. These late freed resources are: - p->percpu_cluster - swap_cgroup_ctrl[type] - block_device setting - inode->i_flags &= ~S_SWAPFILE This patch clears the SWP_USED flag after all its resources are freed, so that swapon can reuse this swap_info by alloc_swap_info() safely. [akpm@linux-foundation.org: tidy up code comment] Signed-off-by: Weijie Yang Acked-by: Hugh Dickins Cc: Krzysztof Kozlowski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- mm/swapfile.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1649,7 +1649,6 @@ SYSCALL_DEFINE1(swapoff, const char __us p->max = 0; swap_map = p->swap_map; p->swap_map = NULL; - p->flags = 0; spin_unlock(&swap_lock); mutex_unlock(&swapon_mutex); vfree(swap_map); @@ -1667,6 +1666,16 @@ SYSCALL_DEFINE1(swapoff, const char __us mutex_unlock(&inode->i_mutex); } filp_close(swap_file, NULL); + + /* + * Clear the SWP_USED flag after all resources are freed so that swapon + * can reuse this swap_info in alloc_swap_info() safely. It is ok to + * not hold p->lock after we cleared its SWP_WRITEOK. + */ + spin_lock(&swap_lock); + p->flags = 0; + spin_unlock(&swap_lock); + err = 0; atomic_inc(&proc_poll_event); wake_up_interruptible(&proc_poll_wait);