[Xen-devel] [PATCH tip/core/rcu 02/20] x86: Use common outgoing-CPU-notification code

["Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

This commit removes the open-coded CPU-offline notification with new
common code.  Among other things, this change avoids calling scheduler
code using RCU from an offline CPU that RCU is ignoring.  It also allows
Xen to notice at online time that the CPU did not go offline correctly.
Note that Xen has the surviving CPU carry out some cleanup operations,
so if the surviving CPU times out, these cleanup operations might have
been carried out while the outgoing CPU was still running.  It might
therefore be unwise to bring this CPU back online, and this commit
avoids doing so.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: <x86@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/cpu.h |  2 --
 arch/x86/include/asm/smp.h |  1 -
 arch/x86/kernel/smpboot.c  | 29 ++++++++---------------------
 arch/x86/xen/smp.c         | 18 ++++++++----------
 4 files changed, 16 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index d2b12988d2ed..bf2caa1dedc5 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -34,8 +34,6 @@ extern int _debug_hotplug_cpu(int cpu, int action);
 #endif
 #endif
 
-DECLARE_PER_CPU(int, cpu_state);
-
 int mwait_usable(const struct cpuinfo_x86 *);
 
 #endif /* _ASM_X86_CPU_H */
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 8cd1cc3bc835..8cd27e08e23c 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -150,7 +150,6 @@ static inline void arch_send_call_function_ipi_mask(const 
struct cpumask *mask)
 }
 
 void cpu_disable_common(void);
-void cpu_die_common(unsigned int cpu);
 void native_smp_prepare_boot_cpu(void);
 void native_smp_prepare_cpus(unsigned int max_cpus);
 void native_smp_cpus_done(unsigned int max_cpus);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index febc6aabc72e..ff24fbd17fe7 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -77,9 +77,6 @@
 #include <asm/realmode.h>
 #include <asm/misc.h>
 
-/* State of each CPU */
-DEFINE_PER_CPU(int, cpu_state) = { 0 };
-
 /* Number of siblings per CPU package */
 int smp_num_siblings = 1;
 EXPORT_SYMBOL(smp_num_siblings);
@@ -257,7 +254,7 @@ static void notrace start_secondary(void *unused)
        lock_vector_lock();
        set_cpu_online(smp_processor_id(), true);
        unlock_vector_lock();
-       per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
+       cpu_set_state_online(smp_processor_id());
        x86_platform.nmi_init();
 
        /* enable local interrupts */
@@ -948,7 +945,10 @@ int native_cpu_up(unsigned int cpu, struct task_struct 
*tidle)
         */
        mtrr_save_state();
 
-       per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
+       /* x86 CPUs take themselves offline, so delayed offline is OK. */
+       err = cpu_check_up_prepare(cpu);
+       if (err && err != -EBUSY)
+               return err;
 
        /* the FPU context is blank, nobody can own it */
        __cpu_disable_lazy_restore(cpu);
@@ -1191,7 +1191,7 @@ void __init native_smp_prepare_boot_cpu(void)
        switch_to_new_gdt(me);
        /* already set me in cpu_online_mask in boot_cpu_init() */
        cpumask_set_cpu(me, cpu_callout_mask);
-       per_cpu(cpu_state, me) = CPU_ONLINE;
+       cpu_set_state_online(me);
 }
 
 void __init native_smp_cpus_done(unsigned int max_cpus)
@@ -1318,14 +1318,10 @@ static void __ref remove_cpu_from_maps(int cpu)
        numa_remove_cpu(cpu);
 }
 
-static DEFINE_PER_CPU(struct completion, die_complete);
-
 void cpu_disable_common(void)
 {
        int cpu = smp_processor_id();
 
-       init_completion(&per_cpu(die_complete, smp_processor_id()));
-
        remove_siblinginfo(cpu);
 
        /* It's now safe to remove this processor from the online map */
@@ -1349,19 +1345,12 @@ int native_cpu_disable(void)
        return 0;
 }
 
-void cpu_die_common(unsigned int cpu)
-{
-       wait_for_completion_timeout(&per_cpu(die_complete, cpu), HZ);
-}
-
 void native_cpu_die(unsigned int cpu)
 {
        /* We don't do anything here: idle task is faking death itself. */
 
-       cpu_die_common(cpu);
-
        /* They ack this in play_dead() by setting CPU_DEAD */
-       if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
+       if (cpu_wait_death(cpu, 5)) {
                if (system_state == SYSTEM_RUNNING)
                        pr_info("CPU %u is now offline\n", cpu);
        } else {
@@ -1375,10 +1364,8 @@ void play_dead_common(void)
        reset_lazy_tlbstate();
        amd_e400_remove_cpu(raw_smp_processor_id());
 
-       mb();
        /* Ack it */
-       __this_cpu_write(cpu_state, CPU_DEAD);
-       complete(&per_cpu(die_complete, smp_processor_id()));
+       (void)cpu_report_death();
 
        /*
         * With physical CPU hotplug, we should halt the cpu
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 08e8489c47f1..e2c7389c58c5 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -90,14 +90,10 @@ static void cpu_bringup(void)
 
        set_cpu_online(cpu, true);
 
-       this_cpu_write(cpu_state, CPU_ONLINE);
-
-       wmb();
+       cpu_set_state_online(cpu);  /* Implies full memory barrier. */
 
        /* We can take interrupts now: we're officially "up". */
        local_irq_enable();
-
-       wmb();                  /* make sure everything is out */
 }
 
 /*
@@ -459,7 +455,10 @@ static int xen_cpu_up(unsigned int cpu, struct task_struct 
*idle)
        xen_setup_timer(cpu);
        xen_init_lock_cpu(cpu);
 
-       per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
+       /* Xen outgoing CPUs need help cleaning up, so -EBUSY is an error. */
+       rc = cpu_check_up_prepare(cpu);
+       if (rc)
+               return rc;
 
        /* make sure interrupts start blocked */
        per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;
@@ -479,10 +478,8 @@ static int xen_cpu_up(unsigned int cpu, struct task_struct 
*idle)
        rc = HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL);
        BUG_ON(rc);
 
-       while(per_cpu(cpu_state, cpu) != CPU_ONLINE) {
+       while (cpu_report_state(cpu) != CPU_ONLINE)
                HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
-               barrier();
-       }
 
        return 0;
 }
@@ -511,7 +508,8 @@ static void xen_cpu_die(unsigned int cpu)
                schedule_timeout(HZ/10);
        }
 
-       cpu_die_common(cpu);
+       (void)cpu_wait_death(cpu, 5);
+       /* FIXME: Are the below calls really safe in case of timeout? */
 
        xen_smp_intr_free(cpu);
        xen_uninit_lock_cpu(cpu);
-- 
1.8.1.5


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