From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757428AbaLIP6O (ORCPT ); Tue, 9 Dec 2014 10:58:14 -0500 Received: from andre.telenet-ops.be ([195.130.132.53]:55707 "EHLO andre.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756896AbaLIP6M (ORCPT ); Tue, 9 Dec 2014 10:58:12 -0500 Message-ID: <54871C13.50309@acm.org> Date: Tue, 09 Dec 2014 16:58:11 +0100 From: Bart Van Assche User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Jens Axboe CC: Christoph Hellwig , Robert Elliott , Ming Lei , Alexander Gordeev , linux-kernel Subject: [PATCH 2/6] blk-mq: Avoid that __bt_get_word() wraps multiple times References: <54871BD0.8020305@acm.org> In-Reply-To: <54871BD0.8020305@acm.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If __bt_get_word() is called with last_tag != 0, if the first find_next_zero_bit() fails, if after wrap-around the test_and_set_bit() call fails and find_next_zero_bit() succeeds, if the next test_and_set_bit() call fails and subsequently find_next_zero_bit() does not find a zero bit, then another wrap-around will occur. Avoid this by introducing an additional local variable. Signed-off-by: Bart Van Assche Cc: Christoph Hellwig Cc: Robert Elliott Cc: Ming Lei Cc: Alexander Gordeev Cc: # v3.13+ --- block/blk-mq-tag.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 728b9a4..5a3db28 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -137,6 +137,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx, static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag) { int tag, org_last_tag, end; + bool wrap = last_tag != 0; org_last_tag = last_tag; end = bm->depth; @@ -148,8 +149,9 @@ restart: * We started with an offset, start from 0 to * exhaust the map. */ - if (org_last_tag && last_tag) { - end = last_tag; + if (wrap) { + wrap = false; + end = org_last_tag; last_tag = 0; goto restart; } -- 2.1.2