x86: Use common outgoing-CPU-notification code

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: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: <x86@kernel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: <xen-devel@lists.xenproject.org>

1 files changed, 25 insertions, 21 deletions

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 08e8489c47f1..1c5e760f34ca 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 +455,13 @@ 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;
+        /*
+         * PV VCPUs are always successfully taken down (see 'while' loop
+         * in xen_cpu_die()), 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 +481,8 @@ 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;
 }
@@ -511,11 +511,11 @@ static void xen_cpu_die(unsigned int cpu)
                 schedule_timeout(HZ/10);
         }
 
-        cpu_die_common(cpu);
-
-        xen_smp_intr_free(cpu);
-        xen_uninit_lock_cpu(cpu);
-        xen_teardown_timer(cpu);
+        if (common_cpu_die(cpu) == 0) {
+                xen_smp_intr_free(cpu);
+                xen_uninit_lock_cpu(cpu);
+                xen_teardown_timer(cpu);
+        }
 }
 
 static void xen_play_dead(void) /* used only with HOTPLUG_CPU */
@@ -747,6 +747,16 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
 static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
         int rc;
+
+        /*
+         * This can happen if CPU was offlined earlier and
+         * offlining timed out in common_cpu_die().
+         */
+        if (cpu_report_state(cpu) == CPU_DEAD_FROZEN) {
+                xen_smp_intr_free(cpu);
+                xen_uninit_lock_cpu(cpu);
+        }
+
         /*
          * xen_smp_intr_init() needs to run before native_cpu_up()
          * so that IPI vectors are set up on the booting CPU before
@@ -768,12 +778,6 @@ static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
         return rc;
 }
 
-static void xen_hvm_cpu_die(unsigned int cpu)
-{
-        xen_cpu_die(cpu);
-        native_cpu_die(cpu);
-}
-
 void __init xen_hvm_smp_init(void)
 {
         if (!xen_have_vector_callback)
@@ -781,7 +785,7 @@ void __init xen_hvm_smp_init(void)
         smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
         smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
         smp_ops.cpu_up = xen_hvm_cpu_up;
-        smp_ops.cpu_die = xen_hvm_cpu_die;
+        smp_ops.cpu_die = xen_cpu_die;
         smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
         smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
         smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;