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

[Waiman Long]

On 8/13/25 11:13 PM, Waiman Long wrote:
> 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().

I have a correction. According to commit d74b27d63a8b ("cgroup/cpuset: 
Change cpuset_rwsem and hotplug lock order") , sched_scheduler() can be 
called while holding cpus_hotplug_lock. So we should keep cpuset_lock() 
as it is.

Cheers,
Longman