No, this patch is horrible.
The correct check is num_present_cpus(). There is no need to make the
weird additional_cpus hackery globally available.
Btw, additional_cpus has interesting properties. Providing a negative
number < -1 on the kernel command line - happened due to a typo -
explodes in early boot, which is not really surprising, but should be
sanity checked.
Thanks,
tglx
---------------->
Subject: x86: make UP alternatives switch depend on present cpus
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 05 Oct 2008 16:45:22 +0200
num_possible_cpus() can be > 1 when disabled CPUs have been accounted.
Disabled CPUs are not in the cpu_present_map, so we can use
num_present_cpus() as a safe indicator to switch to UP alternatives.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index fb04e49..a84ac7b 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -444,7 +444,7 @@ void __init alternative_instructions(void)
_text, _etext);
/* Only switch to UP mode if we don't immediately boot others */
- if (num_possible_cpus() == 1 || setup_max_cpus <= 1)
+ if (num_present_cpus() == 1 || setup_max_cpus <= 1)
alternatives_smp_switch(0);
}
#endif
--
