From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940008AbeE1QX7 (ORCPT ); Mon, 28 May 2018 12:23:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:59192 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934591AbeE1KK7 (ORCPT ); Mon, 28 May 2018 06:10:59 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nikolay Borisov , David Sterba , Sasha Levin Subject: [PATCH 3.18 120/185] btrfs: Fix possible softlock on single core machines Date: Mon, 28 May 2018 12:02:41 +0200 Message-Id: <20180528100102.394767341@linuxfoundation.org> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180528100050.700971285@linuxfoundation.org> References: <20180528100050.700971285@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nikolay Borisov [ Upstream commit 1e1c50a929bc9e49bc3f9935b92450d9e69f8158 ] do_chunk_alloc implements a loop checking whether there is a pending chunk allocation and if so causes the caller do loop. Generally this loop is executed only once, however testing with btrfs/072 on a single core vm machines uncovered an extreme case where the system could loop indefinitely. This is due to a missing cond_resched when loop which doesn't give a chance to the previous chunk allocator finish its job. The fix is to simply add the missing cond_resched. Fixes: 6d74119f1a3e ("Btrfs: avoid taking the chunk_mutex in do_chunk_alloc") Signed-off-by: Nikolay Borisov Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/extent-tree.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -3946,6 +3946,7 @@ again: if (wait_for_alloc) { mutex_unlock(&fs_info->chunk_mutex); wait_for_alloc = 0; + cond_resched(); goto again; }