Re: [Patch -v3 4/4] Make reboot_cpuid a kernel parameter.

[Robin Holt <holt@sgi.com>]

On Mon, Apr 15, 2013 at 10:18:31AM -0700, H. Peter Anvin wrote:
> Um... doesn't this break anyone who currently depends on this?

Yes.  That is also why I kept this separate and not tagged for
stable. They would need to start using the more general kernel parameter
to get the same functionality.  Should I have done it differently?

Robin

> 
> Robin Holt <holt@sgi.com> wrote:
> 
> >
> >Moving the reboot=s<##> parameter for x86 to a kernel parameter
> >proper.  I did not find any other arch that was specifying the
> >reboot cpu.
> >
> >Signed-off-by: Robin Holt <holt@sgi.com>
> >To: Ingo Molnar <mingo@redhat.com>
> >To: Russ Anderson <rja@sgi.com>
> >Cc: Shawn Guo <shawn.guo@linaro.org>
> >Cc: Oleg Nesterov <oleg@redhat.com>
> >Cc: Andrew Morton <akpm@linux-foundation.org>
> >Cc: "H. Peter Anvin" <hpa@zytor.com>
> >Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> >Cc: Linus Torvalds <torvalds@linux-foundation.org>
> >Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> >Cc: Michel Lespinasse <walken@google.com>
> >Cc: Oleg Nesterov <oleg@redhat.com>
> >Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >Cc: Paul Mackerras <paulus@samba.org>
> >Cc: Peter Zijlstra <peterz@infradead.org>
> >Cc: Robin Holt <holt@sgi.com>
> >Cc: "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>
> >Cc: Tejun Heo <tj@kernel.org>
> >Cc: the arch/x86 maintainers <x86@kernel.org>
> >Cc: Thomas Gleixner <tglx@linutronix.de>
> >---
> > Documentation/kernel-parameters.txt |  2 ++
> >arch/x86/kernel/reboot.c            | 44
> >++++---------------------------------
> > kernel/reboot.c                     |  8 ++++++-
> > 3 files changed, 13 insertions(+), 41 deletions(-)
> >
> >diff --git a/Documentation/kernel-parameters.txt
> >b/Documentation/kernel-parameters.txt
> >index 4609e81..11ebb48 100644
> >--- a/Documentation/kernel-parameters.txt
> >+++ b/Documentation/kernel-parameters.txt
> >@@ -2597,6 +2597,8 @@ bytes respectively. Such letter suffixes can also
> >be entirely omitted.
> > 			Format: <reboot_mode>[,<reboot_mode2>[,...]]
> > 			See arch/*/kernel/reboot.c or arch/*/kernel/process.c
> > 
> >+	reboot_cpuid=	[KNL] cpuid to use for reboot/halt, etc operations.
> >+
> > 	relax_domain_level=
> > 			[KNL, SMP] Set scheduler's default relax_domain_level.
> > 			See Documentation/cgroups/cpusets.txt.
> >diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> >index 76fa1e9..39af130 100644
> >--- a/arch/x86/kernel/reboot.c
> >+++ b/arch/x86/kernel/reboot.c
> >@@ -49,10 +49,6 @@ int reboot_force;
> >  */
> > static int reboot_default = 1;
> > 
> >-#ifdef CONFIG_SMP
> >-static int reboot_cpu = -1;
> >-#endif
> >-
> > /*
> >  * This is set if we need to go through the 'emergency' path.
> >  * When machine_emergency_restart() is called, we may be on
> >@@ -64,11 +60,10 @@ static int reboot_emergency;
> > bool port_cf9_safe = false;
> > 
> > /*
> >- * reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm |
> >[c]old] | p[ci]
> >+ * reboot=b[ios] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] |
> >p[ci]
> >  * warm   Don't set the cold reboot flag
> >  * cold   Set the cold reboot flag
> >  * bios   Reboot by jumping through the BIOS
> >- * smp    Reboot by executing reset on BSP or other CPU
> >  * triple Force a triple fault (init)
> >  * kbd    Use the keyboard controller. cold reset (default)
> >  * acpi   Use the RESET_REG in the FADT
> >@@ -95,21 +90,6 @@ static int __init reboot_setup(char *str)
> > 			reboot_mode = 0;
> > 			break;
> > 
> >-#ifdef CONFIG_SMP
> >-		case 's':
> >-			if (isdigit(*(str+1))) {
> >-				reboot_cpu = (int) (*(str+1) - '0');
> >-				if (isdigit(*(str+2)))
> >-					reboot_cpu = reboot_cpu*10 + (int)(*(str+2) - '0');
> >-			}
> >-			/*
> >-			 * We will leave sorting out the final value
> >-			 * when we are ready to reboot, since we might not
> >-			 * have detected BSP APIC ID or smp_num_cpu
> >-			 */
> >-			break;
> >-#endif /* CONFIG_SMP */
> >-
> > 		case 'b':
> > 		case 'a':
> > 		case 'k':
> >@@ -614,26 +594,10 @@ void native_machine_shutdown(void)
> > {
> > 	/* Stop the cpus and apics */
> > #ifdef CONFIG_SMP
> >-
> >-	/* The boot cpu is always logical cpu 0 */
> >-	int reboot_cpu_id = 0;
> >-
> >-	/* See if there has been given a command line override */
> >-	if ((reboot_cpu != -1) && (reboot_cpu < nr_cpu_ids) &&
> >-		cpu_online(reboot_cpu))
> >-		reboot_cpu_id = reboot_cpu;
> >-
> >-	/* Make certain the cpu I'm about to reboot on is online */
> >-	if (!cpu_online(reboot_cpu_id))
> >-		reboot_cpu_id = smp_processor_id();
> >-
> >-	/* Make certain I only run on the appropriate processor */
> >-	set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
> >-
> > 	/*
> >-	 * O.K Now that I'm on the appropriate processor, stop all of the
> >-	 * others. Also disable the local irq to not receive the per-cpu
> >-	 * timer interrupt which may trigger scheduler's load balance.
> >+	 * Stop all of the others. Also disable the local irq to
> >+	 * not receive the per-cpu timer interrupt which may trigger
> >+	 * scheduler's load balance.
> > 	 */
> > 	local_irq_disable();
> > 	stop_other_cpus();
> >diff --git a/kernel/reboot.c b/kernel/reboot.c
> >index 187a0d8..9fbab07 100644
> >--- a/kernel/reboot.c
> >+++ b/kernel/reboot.c
> >@@ -8,6 +8,7 @@
> > #include <linux/kexec.h>
> > #include <linux/kmod.h>
> > #include <linux/kmsg_dump.h>
> >+#include <linux/moduleparam.h>
> > #include <linux/reboot.h>
> > #include <linux/syscalls.h>
> > #include <linux/syscore_ops.h>
> >@@ -66,13 +67,18 @@ int unregister_reboot_notifier(struct
> >notifier_block *nb)
> > }
> > EXPORT_SYMBOL(unregister_reboot_notifier);
> > 
> >+int reboot_cpuid;
> >+core_param(reboot_cpuid, reboot_cpuid, int, 0644);
> >+
> > void migrate_to_reboot_cpu(void)
> > {
> > 	/* The boot cpu is always logical cpu 0 */
> >-	int reboot_cpu_id = 0;
> >+	int reboot_cpu_id = reboot_cpuid;
> > 
> > 	/* Make certain the cpu I'm about to reboot on is online */
> > 	if (!cpu_online(reboot_cpu_id))
> >+		reboot_cpu_id = 0;
> >+	if (!cpu_online(reboot_cpu_id))
> > 		reboot_cpu_id = smp_processor_id();
> > 
> > 	/* Prevent races with other tasks migrating this task. */
> 
> -- 
> Sent from my mobile phone. Please excuse brevity and lack of formatting.