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cgroup: adjust criteria for rstat subsystem cpu lock access

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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: JP Kobryn <inwardvessel@gmail.com>
Fixes: 748922dcfa "cgroup: use subsystem-specific rstat locks to avoid contention"
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202505281034.7ae1668d-lkp@intel.com
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
JP Kobryn
2025-05-28 16:51:30 -07:00
committed by Tejun Heo
parent 0f70f5b08a
commit c853d18706
1 changed files with 16 additions and 9 deletions
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25
kernel/cgroup/rstat.c
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@@ -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)