[PATCH] drivers: base: cacheinfo: Ensure cpu hotplug work is done before Intel RDT

[James Morse <james.morse@arm.com>]

The cacheinfo structures are alloced/freed by cpu online/offline
callbacks. Originally these were only used by sysfs to expose the
cache topology to user space. Without any in-kernel dependencies
CPUHP_AP_ONLINE_DYN was an appropriate choice.

resctrl has started using these structures to identify CPUs that
share a cache. It updates its 'domain' structures from cpu
online/offline callbacks. These depend on the cacheinfo structures
(resctrl_online_cpu()->domain_add_cpu()->get_cache_id()->
 get_cpu_cacheinfo()).
These also run as CPUHP_AP_ONLINE_DYN.

Now that there is an in-kernel dependency, move the cacheinfo
work earlier so we know its done before resctrl's CPUHP_AP_ONLINE_DYN
work runs.

Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
I haven't seen any problems because of this. If someone thinks it should
go to stable:
Cc: <stable@vger.kernel.org> #4.10.x

The particular patch that added RDT is:
Fixes: 2264d9c74dda1 ("x86/intel_rdt: Build structures for each resource based on cache topology")

But as this touches a different set of files, I'm not sure how appropriate
a fixes tag is.

 drivers/base/cacheinfo.c   | 3 ++-
 include/linux/cpuhotplug.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index a7359535caf5..b444f89a2041 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -655,7 +655,8 @@ static int cacheinfo_cpu_pre_down(unsigned int cpu)
 
 static int __init cacheinfo_sysfs_init(void)
 {
-	return cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "base/cacheinfo:online",
+	return cpuhp_setup_state(CPUHP_AP_BASE_CACHEINFO_ONLINE,
+				 "base/cacheinfo:online",
 				 cacheinfo_cpu_online, cacheinfo_cpu_pre_down);
 }
 device_initcall(cacheinfo_sysfs_init);
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 6a381594608c..50c893f03c21 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -175,6 +175,7 @@ enum cpuhp_state {
 	CPUHP_AP_WATCHDOG_ONLINE,
 	CPUHP_AP_WORKQUEUE_ONLINE,
 	CPUHP_AP_RCUTREE_ONLINE,
+	CPUHP_AP_BASE_CACHEINFO_ONLINE,
 	CPUHP_AP_ONLINE_DYN,
 	CPUHP_AP_ONLINE_DYN_END		= CPUHP_AP_ONLINE_DYN + 30,
 	CPUHP_AP_X86_HPET_ONLINE,
-- 
2.20.1