[Xen-devel] [PATCH v2] xen: stop_machine: fill fn_result only in case of error.

[gregory.herrero@xxxxxxxxxx]

From: Gregory Herrero <gregory.herrero@xxxxxxxxxx>

When stop_machine_run() is called with NR_CPUS as last argument,
fn_result member must be filled only if an error happens since it is
shared across all cpus.

Assume CPU1 detects an error and set fn_result to -1, then CPU2 doesn't
detect an error and set fn_result to 0. The error detected by CPU1 will
be ignored.

Note that in case multiple failures occur on different CPUs, only the
last error will be reported.

Signed-off-by: Gregory Herrero <gregory.herrero@xxxxxxxxxx>
---
V2:
    - Add more details in commit description. (Jan Beulich)
    - Use write_atomic() when writing fn_result. (Jan Beulich)
---
 xen/common/stop_machine.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/xen/common/stop_machine.c b/xen/common/stop_machine.c
index 304b783aae..e6a4089790 100644
--- a/xen/common/stop_machine.c
+++ b/xen/common/stop_machine.c
@@ -94,6 +94,7 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned 
int cpu)
     stopmachine_data.fn_data = data;
     stopmachine_data.nr_cpus = nr_cpus;
     stopmachine_data.fn_cpu = cpu;
+    stopmachine_data.fn_result = 0;
     atomic_set(&stopmachine_data.done, 0);
     stopmachine_data.state = STOPMACHINE_START;
 
@@ -112,7 +113,11 @@ int stop_machine_run(int (*fn)(void *), void *data, 
unsigned int cpu)
 
     stopmachine_set_state(STOPMACHINE_INVOKE);
     if ( (cpu == smp_processor_id()) || (cpu == NR_CPUS) )
-        stopmachine_data.fn_result = (*fn)(data);
+    {
+        ret = (*fn)(data);
+        if ( ret )
+            write_atomic(&stopmachine_data.fn_result, ret);
+    }
     stopmachine_wait_state();
     ret = stopmachine_data.fn_result;
 
@@ -150,8 +155,11 @@ static void stopmachine_action(unsigned long cpu)
         case STOPMACHINE_INVOKE:
             if ( (stopmachine_data.fn_cpu == smp_processor_id()) ||
                  (stopmachine_data.fn_cpu == NR_CPUS) )
-                stopmachine_data.fn_result =
-                    stopmachine_data.fn(stopmachine_data.fn_data);
+           {
+                int ret = stopmachine_data.fn(stopmachine_data.fn_data);
+                if ( ret )
+                    write_atomic(&stopmachine_data.fn_result, ret);
+           }
             break;
         default:
             break;
-- 
2.11.0


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