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Subject[RFC PATCH v3 08/12] x86: smp: use generic SMP stop common code
Date
Make x86 use the generic SMP-stop logic provided by common code unified
smp_send_stop() function.

Introduce needed arch_smp_stop_call()/arch_smp_cpus_stop_complete()
helpers that implement the backend architectures specific functionalities
previously provided by native_stop_other_cpus(): common logic is now
delegated to common SMP stop code.

Remove arch-specific smp_send_stop(), and redefine original function
native_stop_other_cpus() to rely instead on the unified common code
version of smp_send_stop(): native_stop_other_cpus() is anyway kept
since it is wired to smp_ops.stop_other_cpus() which get called at
reboot time with particular waiting settings.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
Note that in this patch we kept in use the original x86 local handling
of 'stopping_cpu' variable:

atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id());

Instead, common SMP stop code could have been easily extended to keep and
expose to architectures backends such value using some additional helper
like smp_stop_get_stopping_cpu_id().

This has not been addressed in this series.

v2 ---> v3
- added new wait_forever change capabilities
- better handling of x86 reboot_force flag
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/smp.h | 5 ---
arch/x86/kernel/smp.c | 88 +++++++++++++++++++-------------------
3 files changed, 44 insertions(+), 50 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5e8949953660..0bc274426875 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -92,6 +92,7 @@ config X86
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_QUEUED_RWLOCKS
select ARCH_USE_QUEUED_SPINLOCKS
+ select ARCH_USE_COMMON_SMP_STOP
select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
select ARCH_WANTS_DYNAMIC_TASK_STRUCT
select ARCH_WANT_HUGE_PMD_SHARE
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index e15f364efbcc..e937fab6474b 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -67,11 +67,6 @@ extern void set_cpu_sibling_map(int cpu);
#ifdef CONFIG_SMP
extern struct smp_ops smp_ops;

-static inline void smp_send_stop(void)
-{
- smp_ops.stop_other_cpus(0);
-}
-
static inline void stop_other_cpus(void)
{
smp_ops.stop_other_cpus(1);
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index b8d4e9c3c070..7aeb45c512f7 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -147,71 +147,69 @@ static int register_stop_handler(void)

static void native_stop_other_cpus(int wait)
{
- unsigned long flags;
- unsigned long timeout;
-
if (reboot_force)
return;
+ smp_stop_set_wait_forever(wait);
+ /* use common SMP stop code */
+ smp_send_stop();
+}

- /*
- * Use an own vector here because smp_call_function
- * does lots of things not suitable in a panic situation.
- */
-
- /*
- * We start by using the REBOOT_VECTOR irq.
- * The irq is treated as a sync point to allow critical
- * regions of code on other cpus to release their spin locks
- * and re-enable irqs. Jumping straight to an NMI might
- * accidentally cause deadlocks with further shutdown/panic
- * code. By syncing, we give the cpus up to one second to
- * finish their work before we force them off with the NMI.
- */
- if (num_online_cpus() > 1) {
- /* did someone beat us here? */
- if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
- return;
-
- /* sync above data before sending IRQ */
- wmb();
+void arch_smp_stop_call(cpumask_t *cpus, unsigned int attempt_num)
+{
+ static bool saved_wait;

- apic_send_IPI_allbutself(REBOOT_VECTOR);
+ if (attempt_num == 1) {
+ /*
+ * We start by using the REBOOT_VECTOR irq.
+ * The irq is treated as a sync point to allow critical
+ * regions of code on other cpus to release their spin locks
+ * and re-enable irqs. Jumping straight to an NMI might
+ * accidentally cause deadlocks with further shutdown/panic
+ * code. By syncing, we give the cpus up to one second to
+ * finish their work before we force them off with the NMI.
+ */

/*
- * Don't wait longer than a second for IPI completion. The
- * wait request is not checked here because that would
- * prevent an NMI shutdown attempt in case that not all
- * CPUs reach shutdown state.
+ * Don't wait longer than a second for IPI completion.
+ * Wait forever request is explicitly disabled here because
+ * that would prevent an NMI shutdown attempt in case that
+ * not all CPUs reach shutdown state.
*/
- timeout = USEC_PER_SEC;
- while (num_online_cpus() > 1 && timeout--)
- udelay(1);
- }
+ saved_wait = smp_stop_get_wait_settings(NULL);
+ smp_stop_set_wait_forever(false);
+ smp_stop_set_wait_timeout_us(USEC_PER_MSEC);
+
+ /* Used by NMI handler callback to skip the stopping_cpu. */
+ atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id());
+
+ /* sync above data before sending IRQ */
+ wmb();
+ apic->send_IPI_mask(cpus, REBOOT_VECTOR);
+ } else if (attempt_num > 1) {
+ /* if the REBOOT_VECTOR didn't work, try with the NMI */
+ smp_stop_set_wait_forever(saved_wait);
+ /* Don't wait longer than 10 ms when not asked to wait */
+ smp_stop_set_wait_timeout_us(USEC_PER_MSEC * 10);

- /* if the REBOOT_VECTOR didn't work, try with the NMI */
- if (num_online_cpus() > 1) {
/*
* If NMI IPI is enabled, try to register the stop handler
* and send the IPI. In any case try to wait for the other
* CPUs to stop.
*/
if (!smp_no_nmi_ipi && !register_stop_handler()) {
- /* Sync above data before sending IRQ */
+ /* sync above data before sending IRQ */
wmb();

pr_emerg("Shutting down cpus with NMI\n");

- apic_send_IPI_allbutself(NMI_VECTOR);
+ apic->send_IPI_mask(cpus, NMI_VECTOR);
}
- /*
- * Don't wait longer than 10 ms if the caller didn't
- * reqeust it. If wait is true, the machine hangs here if
- * one or more CPUs do not reach shutdown state.
- */
- timeout = USEC_PER_MSEC * 10;
- while (num_online_cpus() > 1 && (wait || timeout--))
- udelay(1);
}
+}
+
+void arch_smp_cpus_stop_complete(void)
+{
+ unsigned long flags;

local_irq_save(flags);
disable_local_APIC();
--
2.17.1
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