linux-kernel - [RFC 10/10] arm64: smp: Make __cpu

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Date:   Mon, 22 Aug 2022 10:15:20 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Phil Auld <pauld@...hat.com>, Rob Herring <robh@...nel.org>,
        Ben Dooks <ben-linux@...ff.org>
Subject: [RFC 10/10] arm64: smp: Make __cpu_disable() parallel

On a dying cpu, take_cpu_down()->__cpu_disable(), which means if the
teardown path supports parallel, __cpu_disable() confront the parallel,
which may ruin cpu_online_mask etc if no extra lock provides the
protection.

At present, the cpumask is protected by cpu_add_remove_lock, that lock
is quite above __cpu_disable(). In order to protect __cpu_disable() from
parrallel in kexec quick reboot path, introducing a local lock
cpumap_lock.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Sudeep Holla <sudeep.holla@....com>
Cc: Phil Auld <pauld@...hat.com>
Cc: Rob Herring <robh@...nel.org>
Cc: Ben Dooks <ben-linux@...ff.org>
To: linux-arm-kernel@...ts.infradead.org
To: linux-kernel@...r.kernel.org
---
 arch/arm64/kernel/smp.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index ffc5d76cf695..fee8879048b0 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -287,6 +287,28 @@ static int op_cpu_disable(unsigned int cpu)
 	return 0;
 }
 
+static DEFINE_SPINLOCK(cpumap_lock);
+
+static void __cpu_clear_maps(unsigned int cpu)
+{
+	/*
+	 * In the case of kexec rebooting, the cpu_add_remove_lock mutex can not protect
+	 */
+	if (kexec_in_progress)
+		spin_lock(&cpumap_lock);
+	remove_cpu_topology(cpu);
+	numa_remove_cpu(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.
+	 */
+	set_cpu_online(cpu, false);
+	if (kexec_in_progress)
+		spin_unlock(&cpumap_lock);
+
+}
+
 /*
  * __cpu_disable runs on the processor to be shutdown.
  */
@@ -299,14 +321,7 @@ int __cpu_disable(void)
 	if (ret)
 		return ret;
 
-	remove_cpu_topology(cpu);
-	numa_remove_cpu(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.
-	 */
-	set_cpu_online(cpu, false);
+	__cpu_clear_maps(cpu);
 	ipi_teardown(cpu);
 
 	/*
-- 
2.31.1