From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18091C49ED7 for ; Fri, 13 Sep 2019 13:21:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E275D206BB for ; Fri, 13 Sep 2019 13:21:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568380879; bh=a87RG2IfDm8y/jeALS+aChFaTmKn6VxACxCU8UBvCG0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=hDSbaDyTnXMvTHyYBSE7c+6illLrfZizVGOU5a1Pm35z//PrN3BUPx57It4crXAxz SuGH7ZgFcoRsT/IAXGCZhgIwtqX05ky7NlBu/4OpAbLsS5gU1+EOkRH4zdomwHR/WZ Efh7x+CigwhZnYtV1WQ751fjRWP3w+DoMFBipsrg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390788AbfIMNVS (ORCPT ); Fri, 13 Sep 2019 09:21:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:50722 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389614AbfIMNVP (ORCPT ); Fri, 13 Sep 2019 09:21:15 -0400 Received: from localhost (unknown [104.132.45.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C7C41206A5; Fri, 13 Sep 2019 13:21:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568380874; bh=a87RG2IfDm8y/jeALS+aChFaTmKn6VxACxCU8UBvCG0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZwDvPbNvFCH7jKxgIBGWZ4CHfVv5EVdLphSG2eRzxJBerwFECeBbGqnCEjaYtJHTq k2Z5JVZbfhMbnFmHtPezUqvNIjQ84gBOokIi1ejlyeixb++XP0Daga6ysW3v+3Rry3 YDlHmKKQGcTmfLFWr3Zqu3enhVNZVEv86eHWoHDk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Coly Li , Jens Axboe Subject: [PATCH 5.2 19/37] bcache: add comments for mutex_lock(&b->write_lock) Date: Fri, 13 Sep 2019 14:07:24 +0100 Message-Id: <20190913130518.607029021@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190913130510.727515099@linuxfoundation.org> References: <20190913130510.727515099@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When accessing or modifying BTREE_NODE_dirty bit, it is not always necessary to acquire b->write_lock. In bch_btree_cache_free() and mca_reap() acquiring b->write_lock is necessary, and this patch adds comments to explain why mutex_lock(&b->write_lock) is necessary for checking or clearing BTREE_NODE_dirty bit there. Signed-off-by: Coly Li Signed-off-by: Jens Axboe --- drivers/md/bcache/btree.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 3fbadf2058a65..9788b2ee6638f 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -655,6 +655,11 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush) up(&b->io_mutex); } + /* + * BTREE_NODE_dirty might be cleared in btree_flush_btree() by + * __bch_btree_node_write(). To avoid an extra flush, acquire + * b->write_lock before checking BTREE_NODE_dirty bit. + */ mutex_lock(&b->write_lock); if (btree_node_dirty(b)) __bch_btree_node_write(b, &cl); @@ -778,6 +783,11 @@ void bch_btree_cache_free(struct cache_set *c) while (!list_empty(&c->btree_cache)) { b = list_first_entry(&c->btree_cache, struct btree, list); + /* + * This function is called by cache_set_free(), no I/O + * request on cache now, it is unnecessary to acquire + * b->write_lock before clearing BTREE_NODE_dirty anymore. + */ if (btree_node_dirty(b)) { btree_complete_write(b, btree_current_write(b)); clear_bit(BTREE_NODE_dirty, &b->flags); -- 2.20.1