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Message-ID: <36685999-17f1-479e-9895-a22ef28bce67@redhat.com>
Date: Sun, 24 Aug 2025 13:07:24 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, tj@...nel.org,
hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next v4 3/3] cpuset: add helpers for cpus read and
cpuset_mutex locks
On 8/18/25 2:41 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
>
> cpuset: add helpers for cpus_read_lock and cpuset_mutex locks.
>
> Replace repetitive locking patterns with new helpers:
> - cpuset_full_lock()
> - cpuset_full_unlock()
>
> This makes the code cleaner and ensures consistent lock ordering.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
> kernel/cgroup/cpuset-internal.h | 2 ++
> kernel/cgroup/cpuset-v1.c | 12 +++----
> kernel/cgroup/cpuset.c | 60 +++++++++++++++++++--------------
> 3 files changed, 40 insertions(+), 34 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index 75b3aef39231..337608f408ce 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -276,6 +276,8 @@ int cpuset_update_flag(cpuset_flagbits_t bit, struct cpuset *cs, int turning_on)
> ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
> char *buf, size_t nbytes, loff_t off);
> int cpuset_common_seq_show(struct seq_file *sf, void *v);
> +void cpuset_full_lock(void);
> +void cpuset_full_unlock(void);
>
> /*
> * cpuset-v1.c
> diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
> index b69a7db67090..12e76774c75b 100644
> --- a/kernel/cgroup/cpuset-v1.c
> +++ b/kernel/cgroup/cpuset-v1.c
> @@ -169,8 +169,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
> cpuset_filetype_t type = cft->private;
> int retval = -ENODEV;
>
> - cpus_read_lock();
> - cpuset_lock();
> + cpuset_full_lock();
> if (!is_cpuset_online(cs))
> goto out_unlock;
>
> @@ -184,8 +183,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
> break;
> }
> out_unlock:
> - cpuset_unlock();
> - cpus_read_unlock();
> + cpuset_full_unlock();
> return retval;
> }
>
> @@ -454,8 +452,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
> cpuset_filetype_t type = cft->private;
> int retval = 0;
>
> - cpus_read_lock();
> - cpuset_lock();
> + cpuset_full_lock();
> if (!is_cpuset_online(cs)) {
> retval = -ENODEV;
> goto out_unlock;
> @@ -498,8 +495,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
> break;
> }
> out_unlock:
> - cpuset_unlock();
> - cpus_read_unlock();
> + cpuset_full_unlock();
> return retval;
> }
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index d5588a1fef60..d29f90a28e1e 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -250,6 +250,12 @@ static struct cpuset top_cpuset = {
>
> static DEFINE_MUTEX(cpuset_mutex);
>
> +/**
> + * cpuset_lock - Acquire the global cpuset mutex
> + *
> + * This locks the global cpuset mutex to prevent modifications to cpuset
> + * hierarchy and configurations. This helper is not enough to make modification.
> + */
> void cpuset_lock(void)
> {
> mutex_lock(&cpuset_mutex);
> @@ -260,6 +266,24 @@ void cpuset_unlock(void)
> mutex_unlock(&cpuset_mutex);
> }
>
> +/**
> + * cpuset_full_lock - Acquire full protection for cpuset modification
> + *
> + * Takes both CPU hotplug read lock (cpus_read_lock()) and cpuset mutex
> + * to safely modify cpuset data.
> + */
> +void cpuset_full_lock(void)
> +{
> + cpus_read_lock();
> + mutex_lock(&cpuset_mutex);
> +}
> +
> +void cpuset_full_unlock(void)
> +{
> + mutex_unlock(&cpuset_mutex);
> + cpus_read_unlock();
> +}
> +
> static DEFINE_SPINLOCK(callback_lock);
>
> void cpuset_callback_lock_irq(void)
> @@ -3233,8 +3257,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
> int retval = -ENODEV;
>
> buf = strstrip(buf);
> - cpus_read_lock();
> - mutex_lock(&cpuset_mutex);
> + cpuset_full_lock();
> if (!is_cpuset_online(cs))
> goto out_unlock;
>
> @@ -3263,8 +3286,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
> if (force_sd_rebuild)
> rebuild_sched_domains_locked();
> out_unlock:
> - mutex_unlock(&cpuset_mutex);
> - cpus_read_unlock();
> + cpuset_full_unlock();
> flush_workqueue(cpuset_migrate_mm_wq);
> return retval ?: nbytes;
> }
> @@ -3367,12 +3389,10 @@ static ssize_t cpuset_partition_write(struct kernfs_open_file *of, char *buf,
> else
> return -EINVAL;
>
> - cpus_read_lock();
> - mutex_lock(&cpuset_mutex);
> + cpuset_full_lock();
> if (is_cpuset_online(cs))
> retval = update_prstate(cs, val);
> - mutex_unlock(&cpuset_mutex);
> - cpus_read_unlock();
> + cpuset_full_unlock();
> return retval ?: nbytes;
> }
>
> @@ -3497,9 +3517,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
> if (!parent)
> return 0;
>
> - cpus_read_lock();
> - mutex_lock(&cpuset_mutex);
> -
> + cpuset_full_lock();
> if (is_spread_page(parent))
> set_bit(CS_SPREAD_PAGE, &cs->flags);
> if (is_spread_slab(parent))
> @@ -3551,8 +3569,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
> cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
> spin_unlock_irq(&callback_lock);
> out_unlock:
> - mutex_unlock(&cpuset_mutex);
> - cpus_read_unlock();
> + cpuset_full_unlock();
> return 0;
> }
>
> @@ -3567,16 +3584,12 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
> {
> struct cpuset *cs = css_cs(css);
>
> - cpus_read_lock();
> - mutex_lock(&cpuset_mutex);
> -
> + cpuset_full_lock();
> if (!cpuset_v2() && is_sched_load_balance(cs))
> cpuset_update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
>
> cpuset_dec();
> -
> - mutex_unlock(&cpuset_mutex);
> - cpus_read_unlock();
> + cpuset_full_unlock();
> }
>
> /*
> @@ -3588,16 +3601,11 @@ static void cpuset_css_killed(struct cgroup_subsys_state *css)
> {
> struct cpuset *cs = css_cs(css);
>
> - cpus_read_lock();
> - mutex_lock(&cpuset_mutex);
> -
> + cpuset_full_lock();
> /* Reset valid partition back to member */
> if (is_partition_valid(cs))
> update_prstate(cs, PRS_MEMBER);
> -
> - mutex_unlock(&cpuset_mutex);
> - cpus_read_unlock();
> -
> + cpuset_full_unlock();
> }
>
> static void cpuset_css_free(struct cgroup_subsys_state *css)
Reviewed-by: Waiman Long <longman@...hat.com>
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