linux-kernel - [PATCH] arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED

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Date:   Wed, 20 Nov 2019 10:42:12 +0000
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Atish Patra <atish.patra@....com>,
        Russell King <linux@...linux.org.uk>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Lukasz Luba <lukasz.luba@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC

Commit ca74b316df96 ("arm: Use common cpu_topology structure and
functions.") changed cpu_coregroup_mask() from the ARM32 specific
implementation in arch/arm/include/asm/topology.h to the one shared
with ARM64 and RISCV in drivers/base/arch_topology.c.

Currently on Arm32 (TC2 w/ CONFIG_SCHED_MC) the task scheduler setup
code (w/ CONFIG_SCHED_DEBUG) shows this during CPU hotplug:

  ERROR: groups don't span domain->span

It happens to CPUs of the cluster of the CPU which gets hot-plugged
out on scheduler domain MC.

Turns out that the shared cpu_coregroup_mask() requires that the
hot-plugged CPU is removed from the core_sibling mask via
remove_cpu_topology(). Otherwise the 'is core_sibling subset of
cpumask_of_node()' doesn't work. In this case the task scheduler has to
deal with cpumask_of_node instead of core_sibling which is wrong on
scheduler domain MC.

e.g. CPU3 hot-plugged out on TC2 [cluster0: 0,3-4 cluster1: 1-2]:

  cpu_coregroup_mask(): CPU3 cpumask_of_node=0-2,4 core_sibling=0,3-4
                                                                  ^
should be:

  cpu_coregroup_mask(): CPU3 cpumask_of_node=0-2,4 core_sibling=0,4

Add remove_cpu_topology() to __cpu_disable() to remove the CPU from the
topology masks in case of a CPU hotplug out operation.

At the same time tweak store_cpu_topology() slightly so it will call
update_siblings_masks() in case of CPU hotplug in operation via
secondary_start_kernel()->smp_store_cpu_info().

This aligns the Arm32 implementation with the Arm64 one.

Fixes: ca74b316df96 ("arm: Use common cpu_topology structure and functions")
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
---
 arch/arm/kernel/smp.c      |  2 ++
 arch/arm/kernel/topology.c | 15 +++++++--------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 4b0bab2607e4..139c0d98fa29 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -240,6 +240,8 @@ int __cpu_disable(void)
 	if (ret)
 		return ret;

+	remove_cpu_topology(cpu);
+
 	/*
 	 * Take this CPU offline.  Once we clear this, we can't return,
 	 * and we must not schedule until we're ready to give up the cpu.
diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 5b9faba03afb..b37b0a340991 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -196,9 +196,8 @@ void store_cpu_topology(unsigned int cpuid)
 	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
 	unsigned int mpidr;

-	/* If the cpu topology has been already set, just return */
-	if (cpuid_topo->core_id != -1)
-		return;
+	if (cpuid_topo->package_id != -1)
+		goto topology_populated;

 	mpidr = read_cpuid_mpidr();

@@ -231,14 +230,14 @@ void store_cpu_topology(unsigned int cpuid)
 		cpuid_topo->package_id = -1;
 	}

-	update_siblings_masks(cpuid);
-
 	update_cpu_capacity(cpuid);

 	pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
-		cpuid, cpu_topology[cpuid].thread_id,
-		cpu_topology[cpuid].core_id,
-		cpu_topology[cpuid].package_id, mpidr);
+		cpuid, cpuid_topo->thread_id, cpuid_topo->core_id,
+		cpuid_topo->package_id, mpidr);
+
+topology_populated:
+	update_siblings_masks(cpuid);
 }

 static inline int cpu_corepower_flags(void)
-- 
2.17.1