linux-kernel - Re: [PATCH] arm64: topology: Fix false warning in counters_read_on

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Message-ID: <aXoJUYDrhuJgkXEr@willie-the-truck>
Date: Wed, 28 Jan 2026 13:04:17 +0000
From: Will Deacon <will@...nel.org>
To: Jie Zhan <zhanjie9@...ilicon.com>
Cc: Sumit Gupta <sumitg@...dia.com>, catalin.marinas@....com,
	zhenglifeng1@...wei.com, viresh.kumar@...aro.org, rafael@...nel.org,
	beata.michalska@....com, pierre.gondois@....com,
	ionela.voinescu@....com, linux-arm-kernel@...ts.infradead.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, treding@...dia.com,
	jonathanh@...dia.com, bbasu@...dia.com
Subject: Re: [PATCH] arm64: topology: Fix false warning in
 counters_read_on_cpu() for same-CPU reads

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@...dia.com>
> 
> Reviewed-by: Jie Zhan <zhanjie9@...ilicon.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 :)

Will