Commit c853d187 authored by JP Kobryn's avatar JP Kobryn Committed by Tejun Heo
Browse files

cgroup: adjust criteria for rstat subsystem cpu lock access 



Previously it was found that on uniprocessor machines the size of
raw_spinlock_t could be zero so a pre-processor conditional was used to
avoid the allocation of ss->rstat_ss_cpu_lock. The conditional did not take
into account cases where lock debugging features were enabled. Cover these
cases along with the original non-smp case by explicitly using the size of
size of the lock type as criteria for allocation/access where applicable.

Signed-off-by: default avatarJP Kobryn <inwardvessel@gmail.com>
Fixes: 748922dc "cgroup: use subsystem-specific rstat locks to avoid contention"
Reported-by: default avatarkernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202505281034.7ae1668d-lkp@intel.com


Reviewed-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 0f70f5b0

kernel/cgroup/rstat.c

+16 −9
Original line number Diff line number Diff line
@@ -47,8 +47,20 @@ static spinlock_t *ss_rstat_lock(struct cgroup_subsys *ss) 


static raw_spinlock_t *ss_rstat_cpu_lock(struct cgroup_subsys *ss, int cpu)

{

	if (ss)

	if (ss) {

		/*

		 * Depending on config, the subsystem per-cpu lock type may be an

		 * empty struct. In enviromnents where this is the case, allocation

		 * of this field is not performed in ss_rstat_init(). Avoid a

		 * cpu-based offset relative to NULL by returning early. When the

		 * lock type is zero in size, the corresponding lock functions are

		 * no-ops so passing them NULL is acceptable.

		 */

		if (sizeof(*ss->rstat_ss_cpu_lock) == 0)

			return NULL;



		return per_cpu_ptr(ss->rstat_ss_cpu_lock, cpu);

	}



	return per_cpu_ptr(&rstat_base_cpu_lock, cpu);

}
@@ -510,20 +522,15 @@ int __init ss_rstat_init(struct cgroup_subsys *ss) 
{

	int cpu;



#ifdef CONFIG_SMP

	/*

	 * On uniprocessor machines, arch_spinlock_t is defined as an empty

	 * struct. Avoid allocating a size of zero by having this block

	 * excluded in this case. It's acceptable to leave the subsystem locks

	 * unitialized since the associated lock functions are no-ops in the

	 * non-smp case.

	 * Depending on config, the subsystem per-cpu lock type may be an empty

	 * struct. Avoid allocating a size of zero in this case.

	 */

	if (ss) {

	if (ss && sizeof(*ss->rstat_ss_cpu_lock)) {

		ss->rstat_ss_cpu_lock = alloc_percpu(raw_spinlock_t);

		if (!ss->rstat_ss_cpu_lock)

			return -ENOMEM;

	}

#endif



	spin_lock_init(ss_rstat_lock(ss));

	for_each_possible_cpu(cpu)