[tip: smp/urgent] smp/up: Make smp_call_function_single() match SMP semantics

["tip-bot2 for Paul E. McKenney" <tip-bot2@linutronix.de>]

The following commit has been merged into the smp/urgent branch of tip:

Commit-ID:     1e474b28e78897d0d170fab3b28ba683149cb9ea
Gitweb:        https://git.kernel.org/tip/1e474b28e78897d0d170fab3b28ba683149cb9ea
Author:        Paul E. McKenney <paulmck@kernel.org>
AuthorDate:    Wed, 05 Feb 2020 06:34:09 -08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 07 Feb 2020 15:34:12 +01:00

smp/up: Make smp_call_function_single() match SMP semantics

In CONFIG_SMP=y kernels, smp_call_function_single() returns -ENXIO when
invoked for a non-existent CPU.  In contrast, in CONFIG_SMP=n kernels,
a splat is emitted and smp_call_function_single() otherwise silently
ignores its "cpu" argument, instead pretending that the caller intended
to have something happen on CPU 0.  Given that there is now code that
expects smp_call_function_single() to return an error if a bad CPU was
specified, this difference in semantics needs to be addressed.

Bring the semantics of the CONFIG_SMP=n version of
smp_call_function_single() into alignment with its CONFIG_SMP=y
counterpart.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200205143409.GA7021@paulmck-ThinkPad-P72

---
 kernel/up.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/up.c b/kernel/up.c
index 53144d0..c6f323d 100644
--- a/kernel/up.c
+++ b/kernel/up.c
@@ -14,7 +14,8 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 {
 	unsigned long flags;
 
-	WARN_ON(cpu != 0);
+	if (cpu != 0)
+		return -ENXIO;
 
 	local_irq_save(flags);
 	func(info);