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Subject[PATCH v2] ARM: kexec: Make smp stop calls asynchronous
If a panic is triggered by a hrtimer interrupt all online cpus will be
notified and set offline. But as highlighted by commit 19dbdcb8039c
("smp: Warn on function calls from softirq context") this call should
not be made synchronous with disabled interrupts:

softdog: Initiating panic
Kernel panic - not syncing: Software Watchdog Timer expired
WARNING: CPU: 1 PID: 0 at kernel/smp.c:753 smp_call_function_many_cond
unwind_backtrace:
show_stack
dump_stack_lvl
__warn
warn_slowpath_fmt
smp_call_function_many_cond
smp_call_function
crash_smp_send_stop.part.0
machine_crash_shutdown
__crash_kexec
panic
softdog_fire
__hrtimer_run_queues
hrtimer_interrupt

Make the smp call for machine_crash_nonpanic_core() asynchronous.

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
---
Changes in v2:
- Fixed commit msg typo "noitfied" => "notified"
- Link to v1: https://lore.kernel.org/r/20230615-arm-smp-call-async-v1-1-58f4afb20f0f@axis.com
---
arch/arm/kernel/machine_kexec.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 46364b699cc3..5d07cf9e0044 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -94,16 +94,28 @@ static void machine_crash_nonpanic_core(void *unused)
}
}

+static DEFINE_PER_CPU(call_single_data_t, cpu_stop_csd) =
+ CSD_INIT(machine_crash_nonpanic_core, NULL);
+
void crash_smp_send_stop(void)
{
static int cpus_stopped;
unsigned long msecs;
+ call_single_data_t *csd;
+ int cpu, this_cpu = raw_smp_processor_id();

if (cpus_stopped)
return;

atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
- smp_call_function(machine_crash_nonpanic_core, NULL, false);
+ for_each_online_cpu(cpu) {
+ if (cpu == this_cpu)
+ continue;
+
+ csd = &per_cpu(cpu_stop_csd, cpu);
+ smp_call_function_single_async(cpu, csd);
+ }
+
msecs = 1000; /* Wait at most a second for the other cpus to stop */
while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
mdelay(1);
---
base-commit: 52a93d39b17dc7eb98b6aa3edb93943248e03b2f
change-id: 20230807-arm-smp-call-async-4c1da2de9621
Best regards,
--
Mårten Lindahl <marten.lindahl@axis.com>

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