[PATCH] MIPS: SMP: Move the AP sync point before the non-parallel aware functions

[Gregory CLEMENT]

When CONFIG_HOTPLUG_PARALLEL is enabled, the code executing before
cpuhp_ap_sync_alive() is executed in parallel, while after it is
serialized. The functions set_cpu_sibling_map() and set_cpu_core_map()
were not designed to be executed in parallel, so by moving the
cpuhp_ap_sync_alive() before cpuhp_ap_sync_alive(), we then ensure
they will be called serialized.

The measurement done on EyeQ5 did not show any relevant boot time
increase after applying this patch.

Reported-by: Huacai Chen <chenhuacai@xxxxxxxxxx>
Signed-off-by: Gregory CLEMENT <gregory.clement@xxxxxxxxxxx>
---
Hello,

As discussed last week [1], this is the patch that fixes the potential
issue with the functions set_cpu_sibling_map() and set_cpu_core_map().

Gregory

[1]: https://lore.kernel.org/all/aBVBHFGH2kICjnT3@xxxxxxxxxxxxxxxx/
---
 arch/mips/kernel/smp.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 1726744f2b2ec10a44420a7b9b9cd04f06c4d2f6..7901b59d8f60eddefc020cf2a137716af963f09e 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -374,13 +374,13 @@ asmlinkage void start_secondary(void)
 	calibrate_delay();
 	cpu_data[cpu].udelay_val = loops_per_jiffy;
 
+#ifdef CONFIG_HOTPLUG_PARALLEL
+	cpuhp_ap_sync_alive();
+#endif
 	set_cpu_sibling_map(cpu);
 	set_cpu_core_map(cpu);
 
 	cpumask_set_cpu(cpu, &cpu_coherent_mask);
-#ifdef CONFIG_HOTPLUG_PARALLEL
-	cpuhp_ap_sync_alive();
-#endif
 	notify_cpu_starting(cpu);
 
 #ifndef CONFIG_HOTPLUG_PARALLEL

---
base-commit: 3b3704261e851e25983860e4c352f1f73786f4ab
change-id: 20250505-hotplug-paralell-fix-25224cd229c6

Best regards,
-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com