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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/04/2015 10:25 AM, Paul E. McKenney wrote:
> On Wed, Mar 04, 2015 at 09:55:11AM -0500, Boris Ostrovsky wrote:
> > The simple solution is to stop calling native_cpu_die() above but
> > I'd like to use common code in native_cpu_die(). I'll see if I can
> > carve it out without too much damage to x86.
> Very good, thank you!  I look forward to seeing your patch.


How about something like this, on top of your original 02/20 patch (this 
is copy-paste but hopefully it can be applied):

 arch/x86/include/asm/smp.h |    1 +
 arch/x86/kernel/smpboot.c  |   12 +++++++++++-
 arch/x86/xen/smp.c         |   34 ++++++++++++++++++++--------------
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 8cd27e0..a5cb4f6 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -155,6 +155,7 @@ void native_smp_prepare_cpus(unsigned int max_cpus);
 void native_smp_cpus_done(unsigned int max_cpus);
 int native_cpu_up(unsigned int cpunum, struct task_struct *tidle);
 int native_cpu_disable(void);
+int common_cpu_die(unsigned int cpu);
 void native_cpu_die(unsigned int cpu);
 void native_play_dead(void);
 void play_dead_common(void);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ff24fbd..c8fa349 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1345,8 +1345,10 @@ int native_cpu_disable(void)
        return 0;
 }

-void native_cpu_die(unsigned int cpu)
+int common_cpu_die(unsigned int cpu)
 {
+       int ret = 0;
+
        /* We don't do anything here: idle task is faking death itself. */

        /* They ack this in play_dead() by setting CPU_DEAD */
@@ -1355,7 +1357,15 @@ void native_cpu_die(unsigned int cpu)
                        pr_info("CPU %u is now offline\n", cpu);
        } else {
                pr_err("CPU %u didn't die...\n", cpu);
+               ret = -1;
        }
+
+       return ret;
+}
+
+void native_cpu_die(unsigned int cpu)
+{
+       common_cpu_die(cpu);
 }

 void play_dead_common(void)
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index e2c7389..1c5e760 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -455,7 +455,10 @@ static int xen_cpu_up(unsigned int cpu, struct 
task_struct *idle)
        xen_setup_timer(cpu);
        xen_init_lock_cpu(cpu);

-       /* Xen outgoing CPUs need help cleaning up, so -EBUSY is an error. */
+       /*
+        * 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;
@@ -508,12 +511,11 @@ static void xen_cpu_die(unsigned int cpu)
                schedule_timeout(HZ/10);
        }

-       (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);
-       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 */
@@ -745,6 +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
@@ -766,12 +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)
@@ -779,7 +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;
--
1.7.7.6



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