From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756214AbeATAHP (ORCPT ); Fri, 19 Jan 2018 19:07:15 -0500 Received: from out0-236.mail.aliyun.com ([140.205.0.236]:43515 "EHLO out0-236.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752184AbeATAHG (ORCPT ); Fri, 19 Jan 2018 19:07:06 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R261e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03308;MF=yang.s@alibaba-inc.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---.AOzRRsa_1516406816; Subject: Re: [PATCH 2/2 v3] lib: debugobjects: touch watchdog to avoid softlockup when !CONFIG_PREEMPT To: Thomas Gleixner Cc: longman@redhat.com, LKML , Peter Zijlstra References: <1515023802-54196-1-git-send-email-yang.s@alibaba-inc.com> <1515023802-54196-2-git-send-email-yang.s@alibaba-inc.com> From: "Yang Shi" Message-ID: <1069ca54-818d-591f-1989-a081a9560e2a@alibaba-inc.com> Date: Sat, 20 Jan 2018 08:06:55 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/18/18 1:02 AM, Thomas Gleixner wrote: > On Thu, 18 Jan 2018, Yang Shi wrote: >> On 1/17/18 4:21 AM, Thomas Gleixner wrote: >>> There are two things which can be done here: >>> >>> 1) The collected objects can be put on a global free list and work >>> scheduled to free them piecewise. >> >> I don't get your point here. objects free has already been done in a work. >> free_object() -> schedule_work() > > But it's doing it in a loop for each freed object. > >> Do you mean free all of them out of the for loop in a batch? Then don't call >> free_object() in the for loop? > > Somehing like this: > > diff --git a/lib/debugobjects.c b/lib/debugobjects.c > index 2f5349c6e81a..d36940cdc658 100644 > --- a/lib/debugobjects.c > +++ b/lib/debugobjects.c > @@ -42,6 +42,7 @@ static struct debug_obj obj_static_pool[ODEBUG_POOL_SIZE] __initdata; > static DEFINE_RAW_SPINLOCK(pool_lock); > > static HLIST_HEAD(obj_pool); > +static HLIST_HEAD(obj_to_free); > > static int obj_pool_min_free = ODEBUG_POOL_SIZE; > static int obj_pool_free = ODEBUG_POOL_SIZE; > @@ -714,13 +715,12 @@ EXPORT_SYMBOL_GPL(debug_object_active_state); > static void __debug_check_no_obj_freed(const void *address, unsigned long size) > { > unsigned long flags, oaddr, saddr, eaddr, paddr, chunks; > - struct hlist_node *tmp; > - HLIST_HEAD(freelist); > struct debug_obj_descr *descr; > enum debug_obj_state state; > struct debug_bucket *db; > + struct hlist_node *tmp; > struct debug_obj *obj; > - int cnt; > + int cnt, freed = 0; > > saddr = (unsigned long) address; > eaddr = saddr + size; > @@ -751,21 +751,22 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size) > goto repeat; > default: > hlist_del(&obj->node); > - hlist_add_head(&obj->node, &freelist); > + /* Put them on the freelist */ > + raw_spin_lock_irqsave(&pool_lock, flags); > + hlist_add_head(&obj->node, &obj_to_free); > + raw_spin_lock_irqrestore(&pool_lock, flags); > + freed++; > break; > } > } > raw_spin_unlock_irqrestore(&db->lock, flags); > > - /* Now free them */ > - hlist_for_each_entry_safe(obj, tmp, &freelist, node) { > - hlist_del(&obj->node); > - free_object(obj); > - } > - > if (cnt > debug_objects_maxchain) > debug_objects_maxchain = cnt; > } > + > + if (freed) > + schedule_work(.....); > > The allocation side can look at the free list as well and grab objects from > there if the pool level is low if that happens before the work can do that. Thanks a lot for the example. I'm working on a preliminary patch, will send out for review once I finish my tests. > > >>> >>> 2) We can do a cond_resched() if not in atomic context and interrupts are >>> enabled. >> >> I did try this before I went with touching softlockup watchdog approach. The >> problem is in_atomic() can't tell if it is in atomic context on non-preempt >> kernel. For preempt kernel, it is easy. > > Peter, can we do anything about that? As Peter confirmed, in_atomic() is not functional on !PREEMPT kernel, shall we still use touching softlockup watchdog approach? Thanks, Yang > > Thanks, > > tglx >