From: Zhang Zhen Subject: [PATCH] fs/ext4: fix potential endless loop in ext4_mb_discard_group_preallocations() Date: Mon, 31 Aug 2015 17:46:24 +0800 Message-ID: <55E42270.9040503@huawei.com> References: <1441013790-87948-1-git-send-email-zhenzhang.zhang@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: "linux-ext4@vger.kernel.org" To: "tytso@mit.edu" , Jan Kara , Return-path: Received: from szxga02-in.huawei.com ([119.145.14.65]:55186 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751820AbbHaJqp (ORCPT ); Mon, 31 Aug 2015 05:46:45 -0400 In-Reply-To: <1441013790-87948-1-git-send-email-zhenzhang.zhang@huawei.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: In ext4_mb_discard_group_preallocations(), if free is always less than needed, and some PAs are always used in every loop, it will be endless loop. Here we pick a random value to limit the max number of loop. Signed-off-by: Zhang Zhen --- fs/ext4/mballoc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 34b610e..553fbde 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -3836,6 +3836,7 @@ ext4_mb_discard_group_preallocations(struct super_block *sb, int err; int busy = 0; int free = 0; + int tried = 0; mb_debug(1, "discard preallocation for group %u\n", group); @@ -3886,9 +3887,11 @@ repeat: list_add(&pa->u.pa_tmp_list, &list); } - /* if we still need more blocks and some PAs were used, try again */ - if (free < needed && busy) { + /* if we still need more blocks and some PAs were used, try again, + here 20 is a ramdon value. */ + if (free < needed && busy && tried < 20) { busy = 0; + tried++; ext4_unlock_group(sb, group); cond_resched(); goto repeat; -- 1.9.1 .