From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752172AbaBMCp6 (ORCPT ); Wed, 12 Feb 2014 21:45:58 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:35018 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751242AbaBMCp5 (ORCPT ); Wed, 12 Feb 2014 21:45:57 -0500 Date: Wed, 12 Feb 2014 18:45:07 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Johannes Weiner , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] swapoff tmpfs radix_tree: remember to rcu_read_unlock Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Running fsx on tmpfs with concurrent memhog-swapoff-swapon, lots of BUG: sleeping function called from invalid context at kernel/fork.c:606 in_atomic(): 0, irqs_disabled(): 0, pid: 1394, name: swapoff 1 lock held by swapoff/1394: #0: (rcu_read_lock){.+.+.+}, at: [] radix_tree_locate_item+0x1f/0x2b6 followed by ================================================ [ BUG: lock held when returning to user space! ] 3.14.0-rc1 #3 Not tainted ------------------------------------------------ swapoff/1394 is leaving the kernel with locks still held! 1 lock held by swapoff/1394: #0: (rcu_read_lock){.+.+.+}, at: [] radix_tree_locate_item+0x1f/0x2b6 after which the system recovered nicely. Whoops, I long ago forgot the rcu_read_unlock() on one unlikely branch. Fixes: e504f3fdd63d ("tmpfs radix_tree: locate_item to speed up swapoff") Signed-off-by: Hugh Dickins --- Of course, the truth is that I had been hoping to break Johannes's patchset in mmotm, was thrilled to get this on that, then despondent to realize that the only bug I had found was mine. Surprised I've not seen it before in 2.5 years: tried again on 3.14-rc1, got the same after 25 minutes. Probably not serious enough for -stable, but please can we slip the fix into 3.14 - sorry, Johannes's mm-keep-page-cache-radix-tree-nodes-in-check.patch will need a refresh. lib/radix-tree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- 3.14-rc2/lib/radix-tree.c 2013-11-03 15:41:51.000000000 -0800 +++ linux/lib/radix-tree.c 2014-02-09 21:47:22.688092825 -0800 @@ -1253,8 +1253,10 @@ unsigned long radix_tree_locate_item(str node = indirect_to_ptr(node); max_index = radix_tree_maxindex(node->height); - if (cur_index > max_index) + if (cur_index > max_index) { + rcu_read_unlock(); break; + } cur_index = __locate(node, item, cur_index, &found_index); rcu_read_unlock();