From patchwork Thu Mar 23 00:36:54 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 9640305 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 1258A601E9 for ; Thu, 23 Mar 2017 00:37:14 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 046EA25EA6 for ; Thu, 23 Mar 2017 00:37:14 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id ED5B7284E8; Thu, 23 Mar 2017 00:37:13 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 395D825EA6 for ; Thu, 23 Mar 2017 00:37:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751191AbdCWAhM (ORCPT ); Wed, 22 Mar 2017 20:37:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:56963 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753918AbdCWAhK (ORCPT ); Wed, 22 Mar 2017 20:37:10 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 71F59ABEB; Thu, 23 Mar 2017 00:37:08 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 841BB1E117B; Thu, 23 Mar 2017 01:37:05 +0100 (CET) From: Jan Kara To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Dan Williams , Thiago Jung Bauermann , Tejun Heo , Tahsin Erdogan , Omar Sandoval , Jan Kara Subject: [PATCH 02/10] bdi: Mark congested->bdi as internal Date: Thu, 23 Mar 2017 01:36:54 +0100 Message-Id: <20170323003702.27571-3-jack@suse.cz> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20170323003702.27571-1-jack@suse.cz> References: <20170323003702.27571-1-jack@suse.cz> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP congested->bdi pointer is used only to be able to remove congested structure from bdi->cgwb_congested_tree on structure release. Moreover the pointer can become NULL when we unregister the bdi. Rename the field to __bdi and add a comment to make it more explicit this is internal stuff of memcg writeback code and people should not use the field as such use will be likely race prone. We do not bother with converting congested->bdi to a proper refcounted reference. It will be slightly ugly to special-case bdi->wb.congested to avoid effectively a cyclic reference of bdi to itself and the reference gets cleared from bdi_unregister() making it impossible to reference a freed bdi. Acked-by: Tejun Heo Signed-off-by: Jan Kara --- include/linux/backing-dev-defs.h | 4 +++- mm/backing-dev.c | 10 +++++----- 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index ad955817916d..8fb3dcdebc80 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -54,7 +54,9 @@ struct bdi_writeback_congested { atomic_t refcnt; /* nr of attached wb's and blkg */ #ifdef CONFIG_CGROUP_WRITEBACK - struct backing_dev_info *bdi; /* the associated bdi */ + struct backing_dev_info *__bdi; /* the associated bdi, set to NULL + * on bdi unregistration. For memcg-wb + * internal use only! */ int blkcg_id; /* ID of the associated blkcg */ struct rb_node rb_node; /* on bdi->cgwb_congestion_tree */ #endif diff --git a/mm/backing-dev.c b/mm/backing-dev.c index c6f2a37028c2..12408f86783c 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -438,7 +438,7 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp) return NULL; atomic_set(&new_congested->refcnt, 0); - new_congested->bdi = bdi; + new_congested->__bdi = bdi; new_congested->blkcg_id = blkcg_id; goto retry; @@ -466,10 +466,10 @@ void wb_congested_put(struct bdi_writeback_congested *congested) } /* bdi might already have been destroyed leaving @congested unlinked */ - if (congested->bdi) { + if (congested->__bdi) { rb_erase(&congested->rb_node, - &congested->bdi->cgwb_congested_tree); - congested->bdi = NULL; + &congested->__bdi->cgwb_congested_tree); + congested->__bdi = NULL; } spin_unlock_irqrestore(&cgwb_lock, flags); @@ -752,7 +752,7 @@ static void cgwb_bdi_exit(struct backing_dev_info *bdi) rb_entry(rbn, struct bdi_writeback_congested, rb_node); rb_erase(rbn, &bdi->cgwb_congested_tree); - congested->bdi = NULL; /* mark @congested unlinked */ + congested->__bdi = NULL; /* mark @congested unlinked */ } spin_unlock_irq(&cgwb_lock); }