The "allbutself" cpumask in stop_machine_run() is not needed. Instead
of allocating it on the stack it can easily be avoided.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 xen/common/stop_machine.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/xen/common/stop_machine.c b/xen/common/stop_machine.c
index ce6f5624c4..74d04427bd 100644
--- a/xen/common/stop_machine.c
+++ b/xen/common/stop_machine.c
@@ -69,8 +69,8 @@ static void stopmachine_wait_state(void)
 
 int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 {
-    cpumask_t allbutself;
     unsigned int i, nr_cpus;
+    unsigned int this = smp_processor_id();
     int ret;
 
     BUG_ON(!local_irq_is_enabled());
@@ -79,9 +79,9 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
     if ( !get_cpu_maps() )
         return -EBUSY;
 
-    cpumask_andnot(&allbutself, &cpu_online_map,
-                   cpumask_of(smp_processor_id()));
-    nr_cpus = cpumask_weight(&allbutself);
+    nr_cpus = num_online_cpus();
+    if ( cpu_online(this) )
+        nr_cpus--;
 
     /* Must not spin here as the holder will expect us to be descheduled. */
     if ( !spin_trylock(&stopmachine_lock) )
@@ -100,8 +100,9 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 
     smp_wmb();
 
-    for_each_cpu ( i, &allbutself )
-        tasklet_schedule_on_cpu(&per_cpu(stopmachine_tasklet, i), i);
+    for_each_online_cpu ( i )
+        if ( i != this )
+            tasklet_schedule_on_cpu(&per_cpu(stopmachine_tasklet, i), i);
 
     stopmachine_set_state(STOPMACHINE_PREPARE);
     stopmachine_wait_state();
-- 
2.16.4


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>>> On 31.05.19 at 13:53, <jgross@suse.com> wrote:
> The "allbutself" cpumask in stop_machine_run() is not needed. Instead
> of allocating it on the stack it can easily be avoided.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
with one further remark:

> --- a/xen/common/stop_machine.c
> +++ b/xen/common/stop_machine.c
> @@ -69,8 +69,8 @@ static void stopmachine_wait_state(void)
>  
>  int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
>  {
> -    cpumask_t allbutself;
>      unsigned int i, nr_cpus;
> +    unsigned int this = smp_processor_id();
>      int ret;
>  
>      BUG_ON(!local_irq_is_enabled());
> @@ -79,9 +79,9 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
>      if ( !get_cpu_maps() )
>          return -EBUSY;
>  
> -    cpumask_andnot(&allbutself, &cpu_online_map,
> -                   cpumask_of(smp_processor_id()));
> -    nr_cpus = cpumask_weight(&allbutself);
> +    nr_cpus = num_online_cpus();
> +    if ( cpu_online(this) )
> +        nr_cpus--;
>  
>      /* Must not spin here as the holder will expect us to be descheduled. */
>      if ( !spin_trylock(&stopmachine_lock) )
> @@ -100,8 +100,9 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
>  
>      smp_wmb();
>  
> -    for_each_cpu ( i, &allbutself )
> -        tasklet_schedule_on_cpu(&per_cpu(stopmachine_tasklet, i), i);
> +    for_each_online_cpu ( i )
> +        if ( i != this )
> +            tasklet_schedule_on_cpu(&per_cpu(stopmachine_tasklet, i), i);
>  
>      stopmachine_set_state(STOPMACHINE_PREPARE);
>      stopmachine_wait_state();

A few lines down from here there's another use of smp_processor_id().
If I end up committing this I may take the liberty and also change that
to "this", unless you object.

Jan



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On 31/05/2019 06:06, Jan Beulich wrote:
>>>> On 31.05.19 at 13:53, <jgross@suse.com> wrote:
>> The "allbutself" cpumask in stop_machine_run() is not needed. Instead
>> of allocating it on the stack it can easily be avoided.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

LGTM.  Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

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