UPSTREAM: kernel/sched/psi.c: simplify cgroup_move_task()

The existing code triggered an invalid warning about 'rq' possibly being
used uninitialized.  Instead of doing the silly warning suppression by
initializa it to NULL, refactor the code to bail out early instead.

Warning was:

  kernel/sched/psi.c: In function `cgroup_move_task':
  kernel/sched/psi.c:639:13: warning: `rq' may be used uninitialized in this function [-Wmaybe-uninitialized]

Link: http://lkml.kernel.org/r/20181103183339.8669-1-olof@lixom.net
Fixes: 2ce7135adc9ad ("psi: cgroup support")
Signed-off-by: Olof Johansson <olof@lixom.net>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 8fcb2312d1e3300e81aa871aad00d4c038cfc184)

Bug: 127712811
Test: lmkd in PSI mode
Change-Id: Id989da224a726082e0cfa5d5d9460bf63d448a93
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7cdecfc010af83f1f5d8679536433f288aa847d7..3d7355d7c3e3852a085a2d68de6e7bbc705c5071 100644 (file)
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -633,38 +633,39 @@ void psi_cgroup_free(struct cgroup *cgroup)
  */
 void cgroup_move_task(struct task_struct *task, struct css_set *to)
 {
-       bool move_psi = !psi_disabled;
        unsigned int task_flags = 0;
        struct rq_flags rf;
        struct rq *rq;
 
-       if (move_psi) {
-               rq = task_rq_lock(task, &rf);
+       if (psi_disabled) {
+               /*
+                * Lame to do this here, but the scheduler cannot be locked
+                * from the outside, so we move cgroups from inside sched/.
+                */
+               rcu_assign_pointer(task->cgroups, to);
+               return;
+       }
 
-               if (task_on_rq_queued(task))
-                       task_flags = TSK_RUNNING;
-               else if (task->in_iowait)
-                       task_flags = TSK_IOWAIT;
+       rq = task_rq_lock(task, &rf);
 
-               if (task->flags & PF_MEMSTALL)
-                       task_flags |= TSK_MEMSTALL;
+       if (task_on_rq_queued(task))
+               task_flags = TSK_RUNNING;
+       else if (task->in_iowait)
+               task_flags = TSK_IOWAIT;
 
-               if (task_flags)
-                       psi_task_change(task, task_flags, 0);
-       }
+       if (task->flags & PF_MEMSTALL)
+               task_flags |= TSK_MEMSTALL;
 
-       /*
-        * Lame to do this here, but the scheduler cannot be locked
-        * from the outside, so we move cgroups from inside sched/.
-        */
+       if (task_flags)
+               psi_task_change(task, task_flags, 0);
+
+       /* See comment above */
        rcu_assign_pointer(task->cgroups, to);
 
-       if (move_psi) {
-               if (task_flags)
-                       psi_task_change(task, 0, task_flags);
+       if (task_flags)
+               psi_task_change(task, 0, task_flags);
 
-               task_rq_unlock(rq, task, &rf);
-       }
+       task_rq_unlock(rq, task, &rf);
 }
 #endif /* CONFIG_CGROUPS */