sched: fix nr_uninterruptible accounting of frozen tasks really

commit e3c8ca8336 (sched: do not count frozen tasks toward load) broke
the nr_uninterruptible accounting on freeze/thaw. On freeze the task
is excluded from accounting with a check for (task->flags &
PF_FROZEN), but that flag is cleared before the task is thawed. So
while we prevent that the task with state TASK_UNINTERRUPTIBLE
is accounted to nr_uninterruptible on freeze we decrement
nr_uninterruptible on thaw.

Use a separate flag which is handled by the freezing task itself. Set
it before calling the scheduler with TASK_UNINTERRUPTIBLE state and
clear it after we return from frozen state.

Cc: <stable@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/freezer.c b/kernel/freezer.c
index 2f4936cf7083..bd1d42b17cb2 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -44,12 +44,19 @@ void refrigerator(void)
         recalc_sigpending(); /* We sent fake signal, clean it up */
         spin_unlock_irq(&current->sighand->siglock);
 
+        /* prevent accounting of that task to load */
+        current->flags |= PF_FREEZING;
+
         for (;;) {
                 set_current_state(TASK_UNINTERRUPTIBLE);
                 if (!frozen(current))
                         break;
                 schedule();
         }
+
+        /* Remove the accounting blocker */
+        current->flags &= ~PF_FREEZING;
+
         pr_debug("%s left refrigerator\n", current->comm);
         __set_current_state(save);
 }