From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5CF0C34EF1E for ; Thu, 30 Oct 2025 10:41:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761820900; cv=none; b=Z+ESwovRWyUhx3U1ZLJyyWlo6vFz6WIZX8TbmS/Vbly4f7EQ+Fh8BR4SPK7cU9R1QVsU7P+321sVpq+kMPfEACUmOfydVoLklMLisELfqqeY/BLZNfvpXlSNQfy0zjK48kbfAsBmHOpZte7kLjuaJc2zA51BbUj5rBk5jsnCKrE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761820900; c=relaxed/simple; bh=ojEKgyeudD4YJttphu3pso30dFRXxlk85R6+k2daQ+k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=f7LKQjBYpjFjsWE0CU5nfrlhzWwV2AEYLGwrrg9sNXmtXnvVa6eOIspvd50n46Wh3iej5/9LaQCwx6V7DljPNP3/JmhjNKOcu4jX9R5Q2YxkFYeSOawbHR7HzPv8OhIb/HgSJ2fqma9OIV+RN/YHt2MvNWGhuIvwG2kl09yxUag= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=NEnr+AI6; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NEnr+AI6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761820897; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+ZCSyqPB3zuZXWIJsAcvpEcv5Ytx5KgM73EZ3akhFAg=; b=NEnr+AI6wE7g85sLhbQDhSvljYFN/wWX9sQ7bfBsGvJW6+FbtmMXtarQfx3VHZgS/ugSV4 alWhSdN53+go1JQbxgazWhiamgIq1PFdwyXSHzwazo3um0fi94IDjxG2vyrCFf+38ARve8 +cvinXUADew3y/0SAeVwT8cwH3QgXU8= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-373-eppWd_qdMleE1vKBl06g-g-1; Thu, 30 Oct 2025 06:41:31 -0400 X-MC-Unique: eppWd_qdMleE1vKBl06g-g-1 X-Mimecast-MFC-AGG-ID: eppWd_qdMleE1vKBl06g-g_1761820889 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A799B195606E; Thu, 30 Oct 2025 10:41:28 +0000 (UTC) Received: from localhost (unknown [10.72.112.70]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 06FCF30001A1; Thu, 30 Oct 2025 10:41:25 +0000 (UTC) Date: Thu, 30 Oct 2025 18:41:22 +0800 From: Pingfan Liu To: Waiman Long Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Peter Zijlstra , Juri Lelli , Pierre Gondois , Frederic Weisbecker , Ingo Molnar , Tejun Heo , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider Subject: Re: [PATCHv4 2/2] sched/deadline: Walk up cpuset hierarchy to decide root domain when hot-unplug Message-ID: References: <20251028034357.11055-1-piliu@redhat.com> <20251028034357.11055-2-piliu@redhat.com> <52252077-30cb-4a71-ba2a-1c4ecb36df37@redhat.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <52252077-30cb-4a71-ba2a-1c4ecb36df37@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Wed, Oct 29, 2025 at 11:31:23AM -0400, Waiman Long wrote: > On 10/27/25 11:43 PM, Pingfan Liu wrote: > > *** Bug description *** > > When testing kexec-reboot on a 144 cpus machine with > > isolcpus=managed_irq,domain,1-71,73-143 in kernel command line, I > > encounter the following bug: > > > > [ 97.114759] psci: CPU142 killed (polled 0 ms) > > [ 97.333236] Failed to offline CPU143 - error=-16 > > [ 97.333246] ------------[ cut here ]------------ > > [ 97.342682] kernel BUG at kernel/cpu.c:1569! > > [ 97.347049] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > > [...] > > > > In essence, the issue originates from the CPU hot-removal process, not > > limited to kexec. It can be reproduced by writing a SCHED_DEADLINE > > program that waits indefinitely on a semaphore, spawning multiple > > instances to ensure some run on CPU 72, and then offlining CPUs 1–143 > > one by one. When attempting this, CPU 143 failed to go offline. > > bash -c 'taskset -cp 0 $$ && for i in {1..143}; do echo 0 > /sys/devices/system/cpu/cpu$i/online 2>/dev/null; done' > > > > ` > > *** Issue *** > > Tracking down this issue, I found that dl_bw_deactivate() returned > > -EBUSY, which caused sched_cpu_deactivate() to fail on the last CPU. > > But that is not the fact, and contributed by the following factors: > > When a CPU is inactive, cpu_rq()->rd is set to def_root_domain. For an > > blocked-state deadline task (in this case, "cppc_fie"), it was not > > migrated to CPU0, and its task_rq() information is stale. So its rq->rd > > points to def_root_domain instead of the one shared with CPU0. As a > > result, its bandwidth is wrongly accounted into a wrong root domain > > during domain rebuild. > > > > The key point is that root_domain is only tracked through active rq->rd. > > To avoid using a global data structure to track all root_domains in the > > system, there should be a method to locate an active CPU within the > > corresponding root_domain. > > > > *** Solution *** > > To locate the active cpu, the following rules for deadline > > sub-system is useful > > -1.any cpu belongs to a unique root domain at a given time > > -2.DL bandwidth checker ensures that the root domain has active cpus. > > > > Now, let's examine the blocked-state task P. > > If P is attached to a cpuset that is a partition root, it is > > straightforward to find an active CPU. > > If P is attached to a cpuset that has changed from 'root' to 'member', > > the active CPUs are grouped into the parent root domain. Naturally, the > > CPUs' capacity and reserved DL bandwidth are taken into account in the > > ancestor root domain. (In practice, it may be unsafe to attach P to an > > arbitrary root domain, since that domain may lack sufficient DL > > bandwidth for P.) Again, it is straightforward to find an active CPU in > > the ancestor root domain. > > > > This patch groups CPUs into isolated and housekeeping sets. For the > > housekeeping group, it walks up the cpuset hierarchy to find active CPUs > > in P's root domain and retrieves the valid rd from cpu_rq(cpu)->rd. > > > > Signed-off-by: Pingfan Liu > > Cc: Waiman Long > > Cc: Tejun Heo > > Cc: Johannes Weiner > > Cc: "Michal Koutný" > > Cc: Ingo Molnar > > Cc: Peter Zijlstra > > Cc: Juri Lelli > > Cc: Pierre Gondois > > Cc: Vincent Guittot > > Cc: Dietmar Eggemann > > Cc: Steven Rostedt > > Cc: Ben Segall > > Cc: Mel Gorman > > Cc: Valentin Schneider > > To: cgroups@vger.kernel.org > > To: linux-kernel@vger.kernel.org > > --- > > v3 -> v4: > > rename function with cpuset_ prefix > > improve commit log > > > > include/linux/cpuset.h | 18 ++++++++++++++++++ > > kernel/cgroup/cpuset.c | 26 ++++++++++++++++++++++++++ > > kernel/sched/deadline.c | 30 ++++++++++++++++++++++++------ > > 3 files changed, 68 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > > index 2ddb256187b51..d4da93e51b37b 100644 > > --- a/include/linux/cpuset.h > > +++ b/include/linux/cpuset.h > > @@ -12,6 +12,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -130,6 +131,7 @@ extern void rebuild_sched_domains(void); > > extern void cpuset_print_current_mems_allowed(void); > > extern void cpuset_reset_sched_domains(void); > > +extern void cpuset_get_task_effective_cpus(struct task_struct *p, struct cpumask *cpus); > > /* > > * read_mems_allowed_begin is required when making decisions involving > > @@ -276,6 +278,22 @@ static inline void cpuset_reset_sched_domains(void) > > partition_sched_domains(1, NULL, NULL); > > } > > +static inline void cpuset_get_task_effective_cpus(struct task_struct *p, > > + struct cpumask *cpus) > > +{ > > + const struct cpumask *hk_msk; > > + > > + hk_msk = housekeeping_cpumask(HK_TYPE_DOMAIN); > > + if (housekeeping_enabled(HK_TYPE_DOMAIN)) { > > + if (!cpumask_intersects(p->cpus_ptr, hk_msk)) { > > + /* isolated cpus belong to a root domain */ > > + cpumask_andnot(cpus, cpu_active_mask, hk_msk); > > + return; > > + } > > + } > > + cpumask_and(cpus, cpu_active_mask, hk_msk); > > +} > > + > > static inline void cpuset_print_current_mems_allowed(void) > > { > > } > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > > index 27adb04df675d..6ad88018f1a4e 100644 > > --- a/kernel/cgroup/cpuset.c > > +++ b/kernel/cgroup/cpuset.c > > @@ -1102,6 +1102,32 @@ void cpuset_reset_sched_domains(void) > > mutex_unlock(&cpuset_mutex); > > } > > +/* caller hold RCU read lock */ > > +void cpuset_get_task_effective_cpus(struct task_struct *p, struct cpumask *cpus) > > +{ > > + const struct cpumask *hk_msk; > > + struct cpuset *cs; > > + > > + hk_msk = housekeeping_cpumask(HK_TYPE_DOMAIN); > > + if (housekeeping_enabled(HK_TYPE_DOMAIN)) { > > + if (!cpumask_intersects(p->cpus_ptr, hk_msk)) { > > + /* isolated cpus belong to a root domain */ > > + cpumask_andnot(cpus, cpu_active_mask, hk_msk); > > + return; > > + } > > + } > > + /* In HK_TYPE_DOMAIN, cpuset can be applied */ > > + cs = task_cs(p); > > + while (cs != &top_cpuset) { > > + if (is_sched_load_balance(cs)) > > + break; > > + cs = parent_cs(cs); > > + } > > + > > + /* For top_cpuset, its effective_cpus does not exclude isolated cpu */ > > + cpumask_and(cpus, cs->effective_cpus, hk_msk); > > +} > > + > > It looks like you are trying to find a set of CPUs that are definitely in a > active sched domain. The difference between this version and the > !CONFIG_CPUSETS version in cpuset.h is the going up the cpuset hierarchy to > find one with load balancing enabled. I would suggest you extract just this > part out as a cpuset helper function and put the rests into deadline.c as a > separate helper function without the cpuset prefix. In that way, you don't > create a new housekeeping.h header file. > A good suggestion, thanks! Best Regards, Pingfan