linux-kernel - [PATCH] psi: simplify cgroup_move

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Date:   Sat,  3 Nov 2018 11:33:39 -0700
From:   Olof Johansson <olof@...om.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Olof Johansson <olof@...om.net>
Subject: [PATCH] psi: 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]

Fixes: 2ce7135adc9ad ("psi: cgroup support")
Cc: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Olof Johansson <olof@...om.net>
---
 kernel/sched/psi.c | 43 ++++++++++++++++++++++---------------------
 1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7cdecfc010af..3d7355d7c3e3 100644
--- 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 */
 
-- 
2.11.0