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, 2 insertions, 1 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 16a982e389fb..3ab08e4bb6b8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -209,7 +209,7 @@ extern unsigned long long time_sync_thresh;
                         ((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0)
 #define task_contributes_to_load(task)  \
                                 ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
-                                 (task->flags & PF_FROZEN) == 0)
+                                 (task->flags & PF_FREEZING) == 0)
 
 #define __set_task_state(tsk, state_value)              \
         do { (tsk)->state = (state_value); } while (0)
@@ -1680,6 +1680,7 @@ extern cputime_t task_gtime(struct task_struct *p);
 #define PF_MEMALLOC     0x00000800      /* Allocating memory */
 #define PF_FLUSHER      0x00001000      /* responsible for disk writeback */
 #define PF_USED_MATH    0x00002000      /* if unset the fpu must be initialized before use */
+#define PF_FREEZING     0x00004000      /* freeze in progress. do not account to load */
 #define PF_NOFREEZE     0x00008000      /* this thread should not be frozen */
 #define PF_FROZEN       0x00010000      /* frozen for system suspend */
 #define PF_FSTRANS      0x00020000      /* inside a filesystem transaction */