From patchwork Thu Dec 22 14:33:50 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kemeng Shi X-Patchwork-Id: 13079449 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7CD53C4332F for ; Thu, 22 Dec 2022 06:35:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232013AbiLVGfF (ORCPT ); Thu, 22 Dec 2022 01:35:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235124AbiLVGfC (ORCPT ); Thu, 22 Dec 2022 01:35:02 -0500 Received: from dggsgout11.his.huawei.com (unknown [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 474C21EAC1; Wed, 21 Dec 2022 22:35:01 -0800 (PST) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4Nd0sp3sKZz4f3jLy; Thu, 22 Dec 2022 14:34:54 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.124.27]) by APP1 (Coremail) with SMTP id cCh0CgDH5jCP+qNjzwckAQ--.30442S4; Thu, 22 Dec 2022 14:34:57 +0800 (CST) From: Kemeng Shi To: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jack@suse.cz, kbusch@kernel.org, shikemeng@huaweicloud.com Subject: [PATCH RESEND v2 2/5] sbitmap: remove redundant check in __sbitmap_queue_get_batch Date: Thu, 22 Dec 2022 22:33:50 +0800 Message-Id: <20221222143353.598042-3-shikemeng@huaweicloud.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20221222143353.598042-1-shikemeng@huaweicloud.com> References: <20221222143353.598042-1-shikemeng@huaweicloud.com> MIME-Version: 1.0 X-CM-TRANSID: cCh0CgDH5jCP+qNjzwckAQ--.30442S4 X-Coremail-Antispam: 1UD129KBjvJXoW7KF47Aw45urWUAr4fGry3Arb_yoW8Xr1xpF Wjg34rWr4IqFy2v34DA3WUA3W8t398Cryayrs2g34akw1Dtrn3XrWIkFW3u3W3XF95A3W3 Za1fZasF9rWUXFJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUPSb4IE77IF4wAFF20E14v26ryj6rWUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M280x2IEY4vEnII2IxkI6r1a6r45M2 8IrcIa0xkI8VA2jI8067AKxVWUXwA2048vs2IY020Ec7CjxVAFwI0_Gr0_Xr1l8cAvFVAK 0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2IY67AKxVWDJVCq3wA2z4 x0Y4vE2Ix0cI8IcVCY1x0267AKxVW8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l 84ACjcxK6I8E87Iv6xkF7I0E14v26rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I 8CrVACY4xI64kE6c02F40Ex7xfMcIj6xIIjxv20xvE14v26r1j6r18McIj6I8E87Iv67AK xVWUJVW8JwAm72CE4IkC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64vIr41lF7I21c0EjII2zV CS5cI20VAGYxC7MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E 5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAV WUtwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY 1x0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI 0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7s RNVbyUUUUUU== X-CM-SenderInfo: 5vklyvpphqwq5kxd4v5lfo033gof0z/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Commit fbb564a557809 ("lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()") mentioned that "Checking free bits when setting the target bits. Otherwise, it may reuse the busying bits." This commit add check to make sure all masked bits in word before cmpxchg is zero. Then the existing check after cmpxchg to check any zero bit is existing in masked bits in word is redundant. Actually, old value of word before cmpxchg is stored in val and we will filter out busy bits in val by "(get_mask & ~val)" after cmpxchg. So we will not reuse busy bits methioned in commit fbb564a557809 ("lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()"). Revert new-added check to remove redundant check. Signed-off-by: Kemeng Shi Reviewed-by: Jan Kara --- lib/sbitmap.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index cb5e03a2d65b..11e75f4040fb 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -518,11 +518,9 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags, get_mask = ((1UL << nr_tags) - 1) << nr; val = READ_ONCE(map->word); - do { - if ((val & ~get_mask) != val) - goto next; - } while (!atomic_long_try_cmpxchg(ptr, &val, - get_mask | val)); + while (!atomic_long_try_cmpxchg(ptr, &val, + get_mask | val)) + ; get_mask = (get_mask & ~val) >> nr; if (get_mask) { *offset = nr + (index << sb->shift);