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

[Will Deacon]

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 at nvidia.com>
> > 
> > Reviewed-by: Jie Zhan <zhanjie9 at hisilicon.com>
> > 
> > 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