Merge branch 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull cpu hotplug fixes from Thomas Gleixner:
 "Two fixes for the hotplug state machine code:

   - Move the misplaces smb() in the hotplug thread function to the
     proper place, otherwise a half update control struct could be
     observed

   - Prevent state corruption on error rollback, which causes the state
     to advance by one and as a consequence skip it in the bringup
     sequence"

* 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Prevent state corruption on error rollback
  cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()

1 files changed, 6 insertions, 5 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85ad62e..0097acec1c71 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
         bool bringup = st->bringup;
         enum cpuhp_state state;
 
+        if (WARN_ON_ONCE(!st->should_run))
+                return;
+
         /*
          * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
          * that if we see ->should_run we also see the rest of the state.
          */
         smp_mb();
 
-        if (WARN_ON_ONCE(!st->should_run))
-                return;
-
         cpuhp_lock_acquire(bringup);
 
         if (st->single) {
@@ -916,7 +916,8 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                 ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
                 if (ret) {
                         st->target = prev_state;
-                        undo_cpu_down(cpu, st);
+                        if (st->state < prev_state)
+                                undo_cpu_down(cpu, st);
                         break;
                 }
         }
@@ -969,7 +970,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
          * to do the further cleanups.
          */
         ret = cpuhp_down_callbacks(cpu, st, target);
-        if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
+        if (ret && st->state == CPUHP_TEARDOWN_CPU && st->state < prev_state) {
                 cpuhp_reset_state(st, prev_state);
                 __cpuhp_kick_ap(st);
         }