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Message-ID: <c02dd563-7cfc-404d-80d1-cec934117caf@redhat.com>
Date: Tue, 4 Mar 2025 10:05:54 -0500
From: Waiman Long <llong@...hat.com>
To: 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>,
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
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?
Cheers,
Longman
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