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Subject[PATCH] Remove WARN_ON_ONCE in __smp_call_function_single and smp_call_function_single
The comments of these WARN_ON_ONCE said "Can deadlock when called with
interrupts disabled".
But I didn't find anything that will block this function.

So I think maybe this WARN_ON_ONCE is not need now. So I post a patch for that.

Signed-off-by: Hui Zhu <teawater@gmail.com>
Signed-off-by: Zhu Yanhai <gaoyang.zyh@taobao.com>

--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -303,25 +303,13 @@ int smp_call_function_single(int cpu, sm
.flags = 0,
};
unsigned long flags;
- int this_cpu;
int err = 0;

/*
* prevent preemption and reschedule on another processor,
* as well as CPU removal
*/
- this_cpu = get_cpu();
-
- /*
- * Can deadlock when called with interrupts disabled.
- * We allow cpu's that are not yet online though, as no one else can
- * send smp call function interrupt to this cpu and as such deadlocks
- * can't happen.
- */
- WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
- && !oops_in_progress);
-
- if (cpu == this_cpu) {
+ if (cpu == get_cpu()) {
local_irq_save(flags);
func(info);
local_irq_restore(flags);
@@ -409,17 +397,7 @@ void __smp_call_function_single(int cpu,
unsigned int this_cpu;
unsigned long flags;

- this_cpu = get_cpu();
- /*
- * Can deadlock when called with interrupts disabled.
- * We allow cpu's that are not yet online though, as no one else can
- * send smp call function interrupt to this cpu and as such deadlocks
- * can't happen.
- */
- WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
- && !oops_in_progress);
-
- if (cpu == this_cpu) {
+ if (cpu == get_cpu()) {
local_irq_save(flags);
data->func(data->info);
local_irq_restore(flags);

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