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cgroup: A fix for v6.16-rc1

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rstat per-subsystem split change skipped per-cpu allocation on UP configs;
 however even on UP, depending on config options, the size of the percpu
 struct may not be zero leading to crashes. Fix it by conditionalizing the
 per-cpu area allocation and usage on the size of the per-cpu struct.
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Merge tag 'cgroup-for-6.16-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fix from Tejun Heo:
 "The rstat per-subsystem split change skipped per-cpu allocation on UP
  configs; however even on UP, depending on config options, the size of
  the percpu struct may not be zero leading to crashes.

  Fix it by conditionalizing the per-cpu area allocation and usage on
  the size of the per-cpu struct"

* tag 'cgroup-for-6.16-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: adjust criteria for rstat subsystem cpu lock access
This commit is contained in:
Linus Torvalds 2025-06-03 14:12:36 -07:00
commit def5b099a6
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)