stop_machine: fix error code handling on multiple cpus

Using |= for updating a value which might be updated on several cpus
concurrently will not always work since we need to make sure that the
update happens atomically.
To fix this just use a write if the called function returns an error
code on a cpu. We end up writing the error code of an arbitrary cpu
if multiple ones fail but that should be sufficient.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 6 insertions, 3 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 0e688c6a1a63..8aff79d90ddc 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -66,6 +66,7 @@ static void stop_cpu(struct work_struct *unused)
         enum stopmachine_state curstate = STOPMACHINE_NONE;
         struct stop_machine_data *smdata = &idle;
         int cpu = smp_processor_id();
+        int err;
 
         if (!active_cpus) {
                 if (cpu == first_cpu(cpu_online_map))
@@ -86,9 +87,11 @@ static void stop_cpu(struct work_struct *unused)
                                 hard_irq_disable();
                                 break;
                         case STOPMACHINE_RUN:
-                                /* |= allows error detection if functions on
-                                 * multiple CPUs. */
-                                smdata->fnret |= smdata->fn(smdata->data);
+                                /* On multiple CPUs only a single error code
+                                 * is needed to tell that something failed. */
+                                err = smdata->fn(smdata->data);
+                                if (err)
+                                        smdata->fnret = err;
                                 break;
                         default:
                                 break;