x86/smpboot: Fix cpu_init_udelay=10000 corner case boot parameter misbehavior

For legacy machines cpu_init_udelay defaults to 10,000.
For modern machines it is set to 0.

The user should be able to set cpu_init_udelay to
any value on the cmdline, including 10,000.

Before this patch, that was seen as "unchanged from default"
and thus on a modern machine, the user request was ignored
and the delay was set to 0.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dparsons@brightdsl.net
Cc: shrybman@teksavvy.com
Link: http://lkml.kernel.org/r/de363cdbbcfcca1d22569683f7eb9873e0177251.1444968087.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index e0c198e5f920202bf25fa36e34922d4b0d29d82c..32267ccac3d701bec67bec30d5083d1f307ef168 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -509,7 +509,7 @@ void __inquire_remote_apic(int apicid)
  */
 #define UDELAY_10MS_DEFAULT 10000
 
-static unsigned int init_udelay = UDELAY_10MS_DEFAULT;
+static unsigned int init_udelay = INT_MAX;
 
 static int __init cpu_init_udelay(char *str)
 {
@@ -522,13 +522,16 @@ early_param("cpu_init_udelay", cpu_init_udelay);
 static void __init smp_quirk_init_udelay(void)
 {
        /* if cmdline changed it from default, leave it alone */
-       if (init_udelay != UDELAY_10MS_DEFAULT)
+       if (init_udelay != INT_MAX)
                return;
 
        /* if modern processor, use no delay */
        if (((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) && (boot_cpu_data.x86 == 6)) ||
            ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86 >= 0xF)))
                init_udelay = 0;
+
+       /* else, use legacy delay */
+       init_udelay = UDELAY_10MS_DEFAULT;
 }
 
 /*