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cgroup: avoid per-cpu allocation of size zero rstat cpu locks

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Subsystem rstat locks are dynamically allocated per-cpu. It was discovered
that a panic can occur during this allocation when the lock size is zero.
This is the case on non-smp systems, since arch_spinlock_t is defined as an
empty struct. Prevent this allocation when !CONFIG_SMP by adding a
pre-processor conditional around the affected block.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Reported-by: Klara Modin <klarasmodin@gmail.com>
Fixes: 748922dcfa ("cgroup: use subsystem-specific rstat locks to avoid contention")
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
JP Kobryn 2025-05-21 18:32:02 -07:00 committed by Tejun Heo
parent dc9f08bac2
commit 731bdd9746
1 changed files with 9 additions and 0 deletions
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9
kernel/cgroup/rstat.c
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@ -510,11 +510,20 @@ 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.
*/
if (ss) {
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)