From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754007AbbGBAxr (ORCPT ); Wed, 1 Jul 2015 20:53:47 -0400 Received: from mail-qk0-f176.google.com ([209.85.220.176]:36661 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbbGBAxk (ORCPT ); Wed, 1 Jul 2015 20:53:40 -0400 Date: Wed, 1 Jul 2015 20:53:37 -0400 From: Tejun Heo To: Jens Axboe Cc: linux-kernel@vger.kernel.org, Jon Christopherson Subject: [PATCH 2/2 block/for-linus] writeback: don't drain bdi_writeback_congested on bdi destruction Message-ID: <20150702005337.GB26440@mtj.duckdns.org> References: <20150702005253.GA26440@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150702005253.GA26440@mtj.duckdns.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") made bdi (backing_dev_info) host per-cgroup wb's (bdi_writeback's). As the congested state needs to be per-wb and referenced from blkcg side and multiple wbs, the patch made all non-root cong's (bdi_writeback_congested's) reference counted and indexed on bdi. When a bdi is destroyed, cgwb_bdi_destroy() tries to drain all non-root cong's; however, this can hang indefinitely because wb's can also be referenced from blkcg_gq's which are destroyed after bdi destruction is complete. This patch fixes the bug by updating bdi destruction to not wait for cong's to drain. A cong is unlinked from bdi->cgwb_congested_tree on bdi destuction regardless of its reference count as the bdi may go away any point after destruction. wb_congested_put() checks whether the cong is already unlinked on release. Signed-off-by: Tejun Heo Reported-by: Jon Christopherson Link: https://bugzilla.kernel.org/show_bug.cgi?id=100681 Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") --- mm/backing-dev.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -425,7 +425,6 @@ retry: new_congested = NULL; rb_link_node(&congested->rb_node, parent, node); rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree); - atomic_inc(&bdi->usage_cnt); goto found; } @@ -456,7 +455,6 @@ found: */ void wb_congested_put(struct bdi_writeback_congested *congested) { - struct backing_dev_info *bdi = congested->bdi; unsigned long flags; local_irq_save(flags); @@ -465,12 +463,15 @@ void wb_congested_put(struct bdi_writeba return; } - rb_erase(&congested->rb_node, &congested->bdi->cgwb_congested_tree); + /* bdi might already have been destroyed leaving @congested unlinked */ + if (congested->bdi) { + rb_erase(&congested->rb_node, + &congested->bdi->cgwb_congested_tree); + congested->bdi = NULL; + } + spin_unlock_irqrestore(&cgwb_lock, flags); kfree(congested); - - if (atomic_dec_and_test(&bdi->usage_cnt)) - wake_up_all(&cgwb_release_wait); } static void cgwb_release_workfn(struct work_struct *work) @@ -675,13 +676,22 @@ static int cgwb_bdi_init(struct backing_ static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { struct radix_tree_iter iter; + struct bdi_writeback_congested *congested, *congested_n; void **slot; WARN_ON(test_bit(WB_registered, &bdi->wb.state)); spin_lock_irq(&cgwb_lock); + radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0) cgwb_kill(*slot); + + rbtree_postorder_for_each_entry_safe(congested, congested_n, + &bdi->cgwb_congested_tree, rb_node) { + rb_erase(&congested->rb_node, &bdi->cgwb_congested_tree); + congested->bdi = NULL; /* mark @congested unlinked */ + } + spin_unlock_irq(&cgwb_lock); /*