[PATCH v2] arm64: Reduce verbosity on SMP CPU stop

[Jan Glauber]

On Fri, Apr 15, 2016 at 12:37:06PM +0100, Will Deacon wrote:
> You can remove stop_lock altogether now, right? I also wonder whether
> it would be worth printing out which CPUs are still online in the case where
> we fail to stop all the secondaries?

Sorry, I've been a bit offline. Yes, the stop_lock can also be removed. 

How about below patch that prints the CPU ids for all CPUs that failed
to stop?

Jan

--------------------------------

When CPUs are stopped during an abnormal operation like panic
for each CPU a line is printed and the stack trace is dumped.

This information is only interesting for the aborting CPU
and on systems with many CPUs it only makes it harder to
debug if after the aborting CPU the log is flooded with data
about all other CPUs too.

Therefore remove the stack dump and printk of other CPUs
and only print a single line that the other CPUs are going to be
stopped and, in case any CPUs remain online list them.

Signed-off-by: Jan Glauber <jglauber at cavium.com>
---
 arch/arm64/kernel/smp.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index b2d5f4e..29f4e37 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -763,21 +763,11 @@ void arch_irq_work_raise(void)
 }
 #endif
 
-static DEFINE_RAW_SPINLOCK(stop_lock);
-
 /*
  * ipi_cpu_stop - handle IPI from smp_send_stop()
  */
 static void ipi_cpu_stop(unsigned int cpu)
 {
-	if (system_state == SYSTEM_BOOTING ||
-	    system_state == SYSTEM_RUNNING) {
-		raw_spin_lock(&stop_lock);
-		pr_crit("CPU%u: stopping\n", cpu);
-		dump_stack();
-		raw_spin_unlock(&stop_lock);
-	}
-
 	set_cpu_online(cpu, false);
 
 	local_irq_disable();
@@ -872,6 +862,9 @@ void smp_send_stop(void)
 		cpumask_copy(&mask, cpu_online_mask);
 		cpumask_clear_cpu(smp_processor_id(), &mask);
 
+		if (system_state == SYSTEM_BOOTING ||
+		    system_state == SYSTEM_RUNNING)
+			pr_crit("SMP: stopping secondary CPUs\n");
 		smp_cross_call(&mask, IPI_CPU_STOP);
 	}
 
@@ -881,7 +874,8 @@ void smp_send_stop(void)
 		udelay(1);
 
 	if (num_online_cpus() > 1)
-		pr_warning("SMP: failed to stop secondary CPUs\n");
+		pr_warning("SMP: failed to stop secondary CPUs %*pbl\n",
+			   cpumask_pr_args(cpu_online_mask));
 }
 
 /*
-- 
1.9.1