[PATCH v3] 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.

Fix this by restructuring the logic: when IRQs are disabled (tick
context), call the function directly for same-CPU reads. Otherwise
use smp_call_function_single().

Fixes: 997c021abc6e ("cpufreq: CPPC: Update FIE arch_freq_scale in ticks for non-PCC regs")
Suggested-by: Will Deacon <will at kernel.org>
Signed-off-by: Sumit Gupta <sumitg at nvidia.com>
---
v2 -> v3:
- If irqs_disabled(), then call directly for same-CPU counter reads.
  Otherwise use smp_call_function_single(). (Will)
- Remove get_cpu()/put_cpu(). (Will)

v1 -> v2:
 - Rebased on v7.0-rc1
 - Updated Fixes tag to match upstream commit SHA

[1] https://lore.kernel.org/lkml/20260127080700.3565546-1-sumitg@nvidia.com/
[2] https://lore.kernel.org/lkml/20260224092714.1242141-1-sumitg@nvidia.com/
---
 arch/arm64/kernel/topology.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 3fe1faab0362..b32f13358fbb 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -400,16 +400,25 @@ 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;
 
-	if (WARN_ON_ONCE(irqs_disabled()))
-		return -EPERM;
-
-	smp_call_function_single(cpu, func, val, 1);
+	if (irqs_disabled()) {
+		/*
+		 * When IRQs are disabled (tick path: sched_tick ->
+		 * topology_scale_freq_tick or cppc_scale_freq_tick), only local
+		 * CPU counter reads are allowed. Remote CPU counter read would
+		 * require smp_call_function_single() which is unsafe with IRQs
+		 * disabled.
+		 */
+		if (WARN_ON_ONCE(cpu != smp_processor_id()))
+			return -EPERM;
+		func(val);
+	} else {
+		smp_call_function_single(cpu, func, val, 1);
+	}
 
 	return 0;
 }
-- 
2.34.1