Re: [-next v2 4/4] cpuset: add helpers for cpus read and cpuset_mutex locks

[Waiman Long]

On 8/13/25 8:44 PM, Chen Ridong wrote:
> On 2025/8/14 4:09, Waiman Long wrote:
> > On 8/13/25 4:29 AM, Chen Ridong wrote:
> > > From: Chen Ridong <chenridong@xxxxxxxxxx>
> > >
> > > cpuset: add helpers for cpus_read_lock and cpuset_mutex
> > >
> > > Replace repetitive locking patterns with new helpers:
> > > - cpus_read_cpuset_lock()
> > > - cpus_read_cpuset_unlock()
> > >
> > > This makes the code cleaner and ensures consistent lock ordering.
> > >
> > > Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
> > > ---
> > >    kernel/cgroup/cpuset-internal.h |  2 ++
> > >    kernel/cgroup/cpuset-v1.c       | 12 +++------
> > >    kernel/cgroup/cpuset.c          | 48 +++++++++++++++------------------
> > >    3 files changed, 28 insertions(+), 34 deletions(-)
> > >
> > > diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> > > index 75b3aef39231..6fb00c96044d 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 cpus_read_cpuset_lock(void);
> > > +void cpus_read_cpuset_unlock(void);
> > The names are not intuitive. I would prefer just extend the cpuset_lock/unlock to include
> > cpus_read_lock/unlock and we use cpuset_lock/unlock consistently in the cpuset code. Also, there is
> > now no external user of cpuset_lock/unlock, we may as well remove them from include/linux/cpuset.h.
> >
> > Cheers,
> > Longman
> I like the idea and have considered it.
> However, I noticed that cpuset_locked is being used in __sched_setscheduler.

Right, I overloooked the cpuset_lock() call in kernel/sched/syscall.c. 
So we can't remove it from include/linux/cpuset.h.

This call is invoked to ensure cpusets information is stable. However, 
it doesn't hurt if the cpus_read_lock() is also acquired as a result. 
Alternatively, we can use a name like cpuset_full_lock() to include 
cpus_read_lock().

Cheers,
Longman