path: root/arch
diff options
authorStephen Warren <swarren@nvidia.com>2013-06-14 16:14:14 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2013-06-17 21:35:25 +0100
commit19ab428f4b7988ef3ac727c680efc193ef53ce14 (patch)
tree7cdce88e40ca449db2fea719b88a423f884e1157 /arch
parent69f91ff8c93c778cb65b71d9b2d95ff62956354f (diff)
ARM: 7759/1: decouple CPU offlining from reboot/shutdown
Add comments to machine_shutdown()/halt()/power_off()/restart() that describe their purpose and/or requirements re: CPUs being active/not. In machine_shutdown(), replace the call to smp_send_stop() with a call to disable_nonboot_cpus(). This completely disables all but one CPU, thus satisfying the requirement that only a single CPU be active for kexec. Adjust Kconfig dependencies for this change. In machine_halt()/power_off()/restart(), call smp_send_stop() directly, rather than via machine_shutdown(); these functions don't need to completely de-activate all CPUs using hotplug, but rather just quiesce them. Remove smp_kill_cpus(), and its call from smp_send_stop(). smp_kill_cpus() was indirectly calling smp_ops.cpu_kill() without calling smp_ops.cpu_die() on the target CPUs first. At least some implementations of smp_ops had issues with this; it caused cpu_kill() to hang on Tegra, for example. Since smp_send_stop() is only used for shutdown, halt, and power-off, there is no need to attempt any kind of CPU hotplug here. Adjust Kconfig to reflect that machine_shutdown() (and hence kexec) relies upon disable_nonboot_cpus(). However, this alone doesn't guarantee that hotplug will work, or even that hotplug is implemented for a particular piece of HW that a multi-platform zImage runs on. Hence, add error-checking to machine_kexec() to determine whether it did work. Suggested-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Stephen Warren <swarren@nvidia.com> Acked-by: Will Deacon <will.deacon@arm.com> Tested-by: Zhangfei Gao <zhangfei.gao@gmail.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch')
4 files changed, 42 insertions, 20 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 239fa96c12bb..2651b1da1c56 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -2016,7 +2016,7 @@ config XIP_PHYS_ADDR
config KEXEC
bool "Kexec system call (EXPERIMENTAL)"
- depends on (!SMP || HOTPLUG_CPU)
+ depends on (!SMP || PM_SLEEP_SMP)
kexec is a system call that implements the ability to shutdown your
current kernel, and to start another kernel. It is like a reboot
diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 8ef8c9337809..4fb074c446bf 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -134,6 +134,10 @@ void machine_kexec(struct kimage *image)
unsigned long reboot_code_buffer_phys;
void *reboot_code_buffer;
+ if (num_online_cpus() > 1) {
+ pr_err("kexec: error: multiple CPUs still online\n");
+ return;
+ }
page_list = image->head & PAGE_MASK;
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 282de4826abb..6e8931ccf13e 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -184,30 +184,61 @@ int __init reboot_setup(char *str)
__setup("reboot=", reboot_setup);
+ * Called by kexec, immediately prior to machine_kexec().
+ *
+ * This must completely disable all secondary CPUs; simply causing those CPUs
+ * to execute e.g. a RAM-based pin loop is not sufficient. This allows the
+ * kexec'd kernel to use any and all RAM as it sees fit, without having to
+ * avoid any code or data used by any SW CPU pin loop. The CPU hotplug
+ * functionality embodied in disable_nonboot_cpus() to achieve this.
+ */
void machine_shutdown(void)
-#ifdef CONFIG_SMP
- smp_send_stop();
+ disable_nonboot_cpus();
+ * Halting simply requires that the secondary CPUs stop performing any
+ * activity (executing tasks, handling interrupts). smp_send_stop()
+ * achieves this.
+ */
void machine_halt(void)
- machine_shutdown();
+ smp_send_stop();
while (1);
+ * Power-off simply requires that the secondary CPUs stop performing any
+ * activity (executing tasks, handling interrupts). smp_send_stop()
+ * achieves this. When the system power is turned off, it will take all CPUs
+ * with it.
+ */
void machine_power_off(void)
- machine_shutdown();
+ smp_send_stop();
if (pm_power_off)
+ * Restart requires that the secondary CPUs stop performing any activity
+ * while the primary CPU resets the system. Systems with a single CPU can
+ * use soft_restart() as their machine descriptor's .restart hook, since that
+ * will cause the only available CPU to reset. Systems with multiple CPUs must
+ * provide a HW restart implementation, to ensure that all CPUs reset at once.
+ * This is required so that any code running after reset on the primary CPU
+ * doesn't have to co-ordinate with other CPUs to ensure they aren't still
+ * executing pre-reset code, and using RAM that the primary CPU's code wishes
+ * to use. Implementing such co-ordination would be essentially impossible.
+ */
void machine_restart(char *cmd)
- machine_shutdown();
+ smp_send_stop();
arm_pm_restart(reboot_mode, cmd);
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 550d63cef68e..5919eb451bb9 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -651,17 +651,6 @@ void smp_send_reschedule(int cpu)
smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
-static void smp_kill_cpus(cpumask_t *mask)
- unsigned int cpu;
- for_each_cpu(cpu, mask)
- platform_cpu_kill(cpu);
-static void smp_kill_cpus(cpumask_t *mask) { }
void smp_send_stop(void)
unsigned long timeout;
@@ -679,8 +668,6 @@ void smp_send_stop(void)
if (num_online_cpus() > 1)
pr_warning("SMP: failed to stop secondary CPUs\n");
- smp_kill_cpus(&mask);