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

[Sumit Gupta]

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>
---
 arch/arm64/kernel/topology.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 539b38935182..57b71f403007 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -401,12 +401,29 @@ static inline
 int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val)
 {
 	/*
-	 * Abort call on counterless CPU or when interrupts are
-	 * disabled - can lead to deadlock in smp sync call.
+	 * Abort call on counterless CPU.
 	 */
 	if (!cpu_has_amu_feat(cpu))
 		return -EOPNOTSUPP;
 
+	/*
+	 * For same-CPU reads, call the function directly since no IPI
+	 * is needed and this is safe even with IRQs disabled.
+	 * Use get_cpu() to disable preemption as the counter read
+	 * functions call this_cpu_has_cap() which requires a
+	 * non-preemptible context.
+	 */
+	if (cpu == get_cpu()) {
+		func(val);
+		put_cpu();
+		return 0;
+	}
+	put_cpu();
+
+	/*
+	 * Reading from a remote CPU requires IRQs enabled to avoid
+	 * deadlock in smp_call_function_single().
+	 */
 	if (WARN_ON_ONCE(irqs_disabled()))
 		return -EPERM;
 
-- 
2.34.1