[PATCH 4/4] ARM: topology: allocate the cacheinfo early on the boot CPU

[Karl Mehltretter]

ARM secondary CPUs allocate cacheinfo in detect_cache_attributes(),
called from secondary_start_kernel() with interrupts disabled. With
PREEMPT_RT, the allocation takes a sleeping lock and triggers
"BUG: sleeping function called from invalid context".

Call fetch_cache_info() for each possible CPU from init_cpu_topology()
on the boot CPU, following commit 5944ce092b97 ("arch_topology: Build
cacheinfo from primary CPU"). This supplies the arrays before secondary
CPUs populate them. Suppress -ENOENT and -EOPNOTSUPP, which leave cache
detection to the existing late path.

The CLIDR fallback uses the boot CPU's cache geometry. A secondary CPU
with more cache leaves can still require late reallocation and trigger
the warning.

Fixes: a9ff94477836 ("ARM: 9433/2: implement cacheinfo support")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
---
Full warning on QEMU virt, cortex-a15, 7.3-rc2, PREEMPT_RT:

  BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
  in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/1
  Call trace:
   rt_spin_lock from ___slab_alloc+0x68/0x728
   ...
   __kmalloc_noprof from detect_cache_attributes+0xe4/0x734
   detect_cache_attributes from update_siblings_masks+0x10/0x174
   update_siblings_masks from secondary_start_kernel+0xec/0x120

PREEMPT_RT became selectable on ARM in 7.1 with commit c6e61c06d606
("ARM: 9463/1: Allow to enable RT"). The PREEMPT_RT patch queues carry
that change for 6.18 and later, so 6.18.y is affected as well.

QEMU virt, cortex-a15, PREEMPT_RT, 2 and 4 CPUs: the warning is gone,
the cacheinfo sysfs tree is identical before and after, CPU 1 survives
an offline/online cycle. Same on a non-RT build.

QEMU realview-eb-mpcore, ARM11 MPCore, 4 CPUs, ARMv6 plus ARMv7 SMP
kernel with PREEMPT_RT: fetch_cache_info() returns -EOPNOTSUPP through
the CTR format check, no message, no cacheinfo before or after, CPU
hotplug works, kernel messages otherwise identical.

Raspberry Pi 400, four Cortex-A72 CPUs, 32-bit PREEMPT_RT 7.2.6-rc1,
full series: the boot warning is absent and all 12 cache sysfs entries
match the unpatched baseline and earlier topology-only run. The live
DT describes the shared L2, exercising DT-based early allocation.
CPU hotplug is unavailable on this platform.

 arch/arm/kernel/topology.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 2336ee2aa44a..e6b50cd43ce5 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/arch_topology.h>
+#include <linux/cacheinfo.h>
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/cpumask.h>
@@ -238,8 +239,20 @@ void store_cpu_topology(unsigned int cpuid)
  */
 void __init init_cpu_topology(void)
 {
+	int cpu, ret;
+
 	reset_cpu_topology();
 	smp_wmb();
 
 	parse_dt_topology();
+
+	for_each_possible_cpu(cpu) {
+		ret = fetch_cache_info(cpu);
+		if (!ret)
+			continue;
+		/* CPUs without a usable CLIDR return -EOPNOTSUPP. */
+		if (ret != -ENOENT && ret != -EOPNOTSUPP)
+			pr_err("Early cacheinfo failed, ret = %d\n", ret);
+		return;
+	}
 }
-- 
2.53.0