Re: [PATCH] arm64: topology: Fix false warning in counters_read_on_cpu() for same-CPU reads

[Jie Zhan]

On 2/24/2026 2:29 AM, Will Deacon wrote:
> On Wed, Jan 28, 2026 at 01:04:17PM +0000, Will Deacon wrote:
>> On Wed, Jan 28, 2026 at 06:50:42PM +0800, Jie Zhan wrote:
>>> On 1/27/2026 4:07 PM, Sumit Gupta wrote:
>>>> The counters_read_on_cpu() function warns when called with IRQs disabled
>>>> to prevent deadlock in smp_call_function_single(). However, this warning
>>>> is spurious when reading counters on the current CPU since no IPI is
>>>> needed for same-CPU reads.
>>>>
>>>> Commit 12eb8f4fff24 ("cpufreq: CPPC: Update FIE arch_freq_scale in ticks
>>>> for non-PCC regs") changed the CPPC Frequency Invariance Engine to read
>>>> AMU counters directly from the scheduler tick for non-PCC register
>>>> spaces (like FFH), instead of deferring to a kthread. This means
>>>> counters_read_on_cpu() is now called with IRQs disabled from the tick
>>>> handler, triggering the warning:
>>>>
>>>> | WARNING: arch/arm64/kernel/topology.c:410 at counters_read_on_cpu
>>>> | ...
>>>> | Call trace:
>>>> |  counters_read_on_cpu+0x88/0xa8 (P)
>>>> |  cpc_read_ffh+0xdc/0x148
>>>> |  cpc_read+0x260/0x518
>>>> |  cppc_get_perf_ctrs+0xf0/0x398
>>>> |  __cppc_scale_freq_tick+0x4c/0x148 [cppc_cpufreq]
>>>> |  cppc_scale_freq_tick+0x44/0x88 [cppc_cpufreq]
>>>> |  topology_scale_freq_tick+0x34/0x58
>>>> |  sched_tick+0x58/0x300
>>>> |  update_process_times+0xcc/0x120
>>>> |  tick_nohz_handler+0xa8/0x260
>>>> |  __hrtimer_run_queues+0x154/0x360
>>>> |  hrtimer_interrupt+0xf4/0x2b0
>>>> |  arch_timer_handler_phys+0x4c/0x78
>>>> |  ....
>>>> |  CPPC Cpufreq:__cppc_scale_freq_tick: failed to read perf counters
>>>> |  ....
>>>>
>>>> Fix this by calling the counter read function directly for same-CPU
>>>> case, bypassing smp_call_function_single() entirely. Use get_cpu() to
>>>> disable preemption as the counter read functions call this_cpu_has_cap()
>>>> which requires a non-preemptible context.
>>>>
>>>> Fixes: 12eb8f4fff24 ("cpufreq: CPPC: Update FIE arch_freq_scale in ticks for non-PCC regs")
>>>> Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
>>>
>>> Reviewed-by: Jie Zhan <zhanjie9@xxxxxxxxxxxxx>
>>>
>>> Looks fine for me except for the minor comment wrapping.
>>>
>>> Thanks for spotting this.
>>> I may have missed the warning log in the FFH test.
>>>
>>> This happens during the short window in cpufreq_policy_online() between
>>> driver->init() and the CREATE_POLICY notifier that gets AMU FIE ready.
>>> After that, CPPC FIE will be stopped.
>>>
>>> Ideally this can be merged together with Viresh's PR since the CPPC FIE
>>> changes are there.
>>> https://lore.kernel.org/all/j4qdid7iqmng4gzb5ozefemjkep3wx2b5z2yki5tnqc3vzvzf4@kvrnarvdod5p/
>>
>> Right, looks like this should go via Rafael but if it doesn't make the merge
>> window then I can pick it up at -rc1 (please remind me :)
> 
> Looks like this fix is still needed. Please can you post a new version,
> based on -rc1, so that I can pick it up?
> 
> You'll also need to fix the SHA in the commit message and the Fixes: tag,
> as 12eb8f4fff24 doesn't match the upstream change.
> 
> Will
> 
I believe this goes to Sumit because he's the author.

Sumit, can you update this patch?

Jie