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Message-ID: <Z8ci4jq5IhYGkxtk@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 4 Mar 2025 15:57:22 +0000
From: Juri Lelli <juri.lelli@...hat.com>
To: Waiman Long <llong@...hat.com>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
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 2/5] sched/topology: Wrappers for sched_domains_mutex
Hi Waiman,
Thanks for the review!
On 04/03/25 10:05, Waiman Long wrote:
> On 3/4/25 3:40 AM, Juri Lelli wrote:
> > Create wrappers for sched_domains_mutex so that it can transparently be
> > used on both CONFIG_SMP and !CONFIG_SMP, as some function will need to
> > do.
> >
> > Reported-by: Jon Hunter <jonathanh@...dia.com>
> > Fixes: 53916d5fd3c0 ("sched/deadline: Check bandwidth overflow earlier for hotplug")
> > Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
> > ---
> > include/linux/sched.h | 2 ++
> > kernel/cgroup/cpuset.c | 4 ++--
> > kernel/sched/core.c | 4 ++--
> > kernel/sched/debug.c | 8 ++++----
> > kernel/sched/topology.c | 17 +++++++++++++++--
> > 5 files changed, 25 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 9632e3318e0d..d5f8c161d852 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -383,6 +383,8 @@ enum uclamp_id {
> > extern struct root_domain def_root_domain;
> > extern struct mutex sched_domains_mutex;
> > #endif
> > +extern void sched_domains_mutex_lock(void);
> > +extern void sched_domains_mutex_unlock(void);
>
> If all access to sched_domains_mutex is through the wrappers, we may not
> need to expose sched_domains_mutex at all. Also it is more efficient for the
> non-SMP case to put the wrappers inside the CONFIG_SMP block and define the
> empty inline functions in the else part.
>
>
> > struct sched_param {
> > int sched_priority;
> > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> > index 0f910c828973..f87526edb2a4 100644
> > --- a/kernel/cgroup/cpuset.c
> > +++ b/kernel/cgroup/cpuset.c
> > @@ -994,10 +994,10 @@ static void
> > partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
> > struct sched_domain_attr *dattr_new)
> > {
> > - mutex_lock(&sched_domains_mutex);
> > + sched_domains_mutex_lock();
> > partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
> > dl_rebuild_rd_accounting();
> > - mutex_unlock(&sched_domains_mutex);
> > + sched_domains_mutex_unlock();
> > }
> > /*
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9aecd914ac69..7b14500d731b 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -8424,9 +8424,9 @@ void __init sched_init_smp(void)
> > * CPU masks are stable and all blatant races in the below code cannot
> > * happen.
> > */
> > - mutex_lock(&sched_domains_mutex);
> > + sched_domains_mutex_lock();
> > sched_init_domains(cpu_active_mask);
> > - mutex_unlock(&sched_domains_mutex);
> > + sched_domains_mutex_unlock();
> > /* Move init over to a non-isolated CPU */
> > if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_DOMAIN)) < 0)
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index ef047add7f9e..a0893a483d35 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -292,7 +292,7 @@ static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
> > bool orig;
> > cpus_read_lock();
> > - mutex_lock(&sched_domains_mutex);
> > + sched_domains_mutex_lock();
> > orig = sched_debug_verbose;
> > result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
> > @@ -304,7 +304,7 @@ static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
> > sd_dentry = NULL;
> > }
> > - mutex_unlock(&sched_domains_mutex);
> > + sched_domains_mutex_unlock();
> > cpus_read_unlock();
> > return result;
> > @@ -515,9 +515,9 @@ static __init int sched_init_debug(void)
> > debugfs_create_u32("migration_cost_ns", 0644, debugfs_sched, &sysctl_sched_migration_cost);
> > debugfs_create_u32("nr_migrate", 0644, debugfs_sched, &sysctl_sched_nr_migrate);
> > - mutex_lock(&sched_domains_mutex);
> > + sched_domains_mutex_lock();
> > update_sched_domain_debugfs();
> > - mutex_unlock(&sched_domains_mutex);
> > + sched_domains_mutex_unlock();
> > #endif
> > #ifdef CONFIG_NUMA_BALANCING
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index c49aea8c1025..e2b879ec9458 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -6,6 +6,19 @@
> > #include <linux/bsearch.h>
> > DEFINE_MUTEX(sched_domains_mutex);
> > +#ifdef CONFIG_SMP
> > +void sched_domains_mutex_lock(void)
> > +{
> > + mutex_lock(&sched_domains_mutex);
> > +}
> > +void sched_domains_mutex_unlock(void)
> > +{
> > + mutex_unlock(&sched_domains_mutex);
> > +}
> > +#else
> > +void sched_domains_mutex_lock(void) { }
> > +void sched_domains_mutex_unlock(void) { }
> > +#endif
> > /* Protected by sched_domains_mutex: */
> > static cpumask_var_t sched_domains_tmpmask;
> > @@ -2791,7 +2804,7 @@ void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new[],
> > void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
> > struct sched_domain_attr *dattr_new)
> > {
> > - mutex_lock(&sched_domains_mutex);
> > + sched_domains_mutex_lock();
> > partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
> > - mutex_unlock(&sched_domains_mutex);
> > + sched_domains_mutex_unlock();
> > }
>
> There are two "lockdep_assert_held(&sched_domains_mutex);" statements in
> topology.c file and one in cpuset.c. That can be problematic in the non-SMP
> case. Maybe another wrapper to do the assert?
Yes, makes sense. Will modify as you suggest here and above.
Best,
Juri
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