[linux-yocto] [PATCH 16/17] kernel/smp: Allow smp_call_function_single() to be called with a function that doesn't return.

[Charlie Paul]

From: John Jacques <john.jacques at lsi.com>

When we do a reset (core, not chip or system), the core that is doing the reset has to
tell all the other cores to reset.  To do this, we call smp_call_function_single().
In this case the function specified in smp_call_function_single() doesn't return.
The "wait" parameter (third argument, described as '@wait: If true, wait until
function has completed on other CPUs.') doesn't work as described without the patch.

Without the patch, smp_call_function_single() doesn't return when the function
indicated resets the called core.  The comments indicate that it should, but it does not.

Signen-off-by: John Jacques <john.jacques at lsi.com>
---
 kernel/smp.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index d5f3238..040b2b1 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -17,14 +17,14 @@
 static struct {
 	struct list_head	queue;
 	raw_spinlock_t		lock;
-} call_function __cacheline_aligned_in_smp =
-	{
+} call_function __cacheline_aligned_in_smp = {
 		.queue		= LIST_HEAD_INIT(call_function.queue),
 		.lock		= __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),
 	};
 
 enum {
 	CSD_FLAG_LOCK		= 0x01,
+	CSD_FLAG_NOWAIT		= 0x02,
 };
 
 struct call_function_data {
@@ -268,6 +268,8 @@ void generic_smp_call_function_single_interrupt(void)
 
 	while (!list_empty(&list)) {
 		struct call_single_data *data;
+		void (*func)(void *);
+		void *info;
 
 		data = list_entry(list.next, struct call_single_data, list);
 		list_del(&data->list);
@@ -278,12 +280,21 @@ void generic_smp_call_function_single_interrupt(void)
 		 * so save them away before making the call:
 		 */
 		data_flags = data->flags;
-
-		data->func(data->info);
+		func = data->func;
+		info = data->info;
 
 		/*
+		 * Unlock before calling func so that func never has
+		 * to return.
+		 *
 		 * Unlocked CSDs are valid through generic_exec_single():
 		 */
+		if ((data_flags & CSD_FLAG_LOCK) &&
+		    (data_flags & CSD_FLAG_NOWAIT))
+			csd_unlock(data);
+
+		func(info);
+
 		if (data_flags & CSD_FLAG_LOCK)
 			csd_unlock(data);
 	}
@@ -337,6 +348,9 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 
 			csd_lock(data);
 
+			if (!wait)
+				data->flags |= CSD_FLAG_NOWAIT;
+
 			data->func = func;
 			data->info = info;
 			generic_exec_single(cpu, data, wait);
@@ -672,7 +686,7 @@ EXPORT_SYMBOL(nr_cpu_ids);
 /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
 void __init setup_nr_cpu_ids(void)
 {
-	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
+	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask), NR_CPUS) + 1;
 }
 
 /* Called by boot processor to activate the rest. */
-- 
1.7.9.5