linux-kernel - Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting after every update

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Message-ID: <fd4d6143-9bd2-4a7c-80dc-1e19e4d1b2d1@redhat.com>
Date: Mon, 10 Mar 2025 20:16:08 -0400
From: Waiman Long <llong@...hat.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>,
 Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Qais Yousef <qyousef@...alina.io>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Swapnil Sapkal <swapnil.sapkal@....com>,
 Shrikanth Hegde <sshegde@...ux.ibm.com>, Phil Auld <pauld@...hat.com>,
 luca.abeni@...tannapisa.it, tommaso.cucinotta@...tannapisa.it,
 Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting
 after every update

On 3/10/25 3:18 PM, Waiman Long wrote:
>
> On 3/10/25 2:54 PM, Dietmar Eggemann wrote:
>> On 10/03/2025 10:37, Juri Lelli wrote:
>>> Rebuilding of root domains accounting information (total_bw) is
>>> currently broken on some cases, e.g. suspend/resume on aarch64. Problem
>> Nit: Couldn't spot any arch dependency here. I guess it was just tested
>> on Arm64 platforms so far.
>>
>> [...]
>>
>>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>>> index 44093339761c..363ad268a25b 100644
>>> --- a/kernel/sched/topology.c
>>> +++ b/kernel/sched/topology.c
>>> @@ -2791,6 +2791,7 @@ void partition_sched_domains_locked(int 
>>> ndoms_new, cpumask_var_t doms_new[],
>>>       ndoms_cur = ndoms_new;
>>>         update_sched_domain_debugfs();
>>> +    dl_rebuild_rd_accounting();
>> Won't dl_rebuild_rd_accounting()'s lockdep_assert_held(&cpuset_mutex)
>> barf when called via cpuhp's:
>>
>> sched_cpu_deactivate()
>>
>>    cpuset_cpu_inactive()
>>
>>      partition_sched_domains()
>>
>>        partition_sched_domains_locked()
>>
>>          dl_rebuild_rd_accounting()
>>
>> ?
>>
>> [...]
>
> Right. If cpuhp_tasks_frozen is true, partition_sched_domains() will 
> be called without holding cpuset mutex.
>
> Well, I think we will need an additional wrapper in cpuset.c that 
> acquires the cpuset_mutex first before calling 
> partition_sched_domains() and use the new wrapper in these cases.

Actually, partition_sched_domains() is called with the special arguments 
(1, NULL, NULL) to reset the domain to a single one. So perhaps 
something like the following will be enough to avoid this problem.

BTW, we can merge partition_sched_domains_locked() into 
partition_sched_domains() as there is no other caller.

Cheers,
Longman

------------------------------------------------------------------------------------------------

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 95bde793651c..39b9ffa6a39a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2692,6 +2692,7 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
                                     struct sched_domain_attr *dattr_new)
  {
         bool __maybe_unused has_eas = false;
+       bool reset_domain = false;
         int i, j, n;
         int new_topology;

@@ -2706,6 +2707,7 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
         if (!doms_new) {
                 WARN_ON_ONCE(dattr_new);
                 n = 0;
+               reset_domain = true;
                 doms_new = alloc_sched_domains(1);
                 if (doms_new) {
                         n = 1;
@@ -2778,7 +2780,8 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
         ndoms_cur = ndoms_new;

         update_sched_domain_debugfs();
-       dl_rebuild_rd_accounting();
+       if (!reset_domain)
+               dl_rebuild_rd_accounting();
  }

  /*