sched/core: Convert get_task_struct() to return the task

Returning the pointer that was passed in allows us to write
slightly more idiomatic code.  Convert a few users.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190704221323.24290-1-willy@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/task.h

@@ -105,7 +105,11 @@ extern void sched_exec(void);
 #define sched_exec()   {}
 #endif
 
-#define get_task_struct(tsk) do { refcount_inc(&(tsk)->usage); } while(0)
+static inline struct task_struct *get_task_struct(struct task_struct *t)
+{
+	refcount_inc(&t->usage);
+	return t;
+}
 
 extern void __put_task_struct(struct task_struct *t);
 

kernel/events/core.c

@@ -4089,10 +4089,8 @@ alloc_perf_context(struct pmu *pmu, struct task_struct *task)
 		return NULL;
 
 	__perf_event_init_context(ctx);
-	if (task) {
-		ctx->task = task;
-		get_task_struct(task);
-	}
+	if (task)
+		ctx->task = get_task_struct(task);
 	ctx->pmu = pmu;
 
 	return ctx;
@@ -10355,8 +10353,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		 * and we cannot use the ctx information because we need the
 		 * pmu before we get a ctx.
 		 */
-		get_task_struct(task);
-		event->hw.target = task;
+		event->hw.target = get_task_struct(task);
 	}
 
 	event->clock = &local_clock;

kernel/irq/manage.c

@@ -1255,8 +1255,7 @@ setup_irq_thread(struct irqaction *new, unsigned int irq, bool secondary)
 	 * the thread dies to avoid that the interrupt code
 	 * references an already freed task_struct.
 	 */
-	get_task_struct(t);
-	new->thread = t;
+	new->thread = get_task_struct(t);
 	/*
 	 * Tell the thread to set its affinity. This is
 	 * important for shared interrupt handlers as we do

kernel/locking/rtmutex.c

@@ -628,8 +628,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 		}
 
 		/* [10] Grab the next task, i.e. owner of @lock */
-		task = rt_mutex_owner(lock);
-		get_task_struct(task);
+		task = get_task_struct(rt_mutex_owner(lock));
 		raw_spin_lock(&task->pi_lock);
 
 		/*
@@ -709,8 +708,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 	}
 
 	/* [10] Grab the next task, i.e. the owner of @lock */
-	task = rt_mutex_owner(lock);
-	get_task_struct(task);
+	task = get_task_struct(rt_mutex_owner(lock));
 	raw_spin_lock(&task->pi_lock);
 
 	/* [11] requeue the pi waiters if necessary */

kernel/trace/trace_sched_wakeup.c

@@ -579,8 +579,7 @@ probe_wakeup(void *ignore, struct task_struct *p)
 	else
 		tracing_dl = 0;
 
-	wakeup_task = p;
-	get_task_struct(wakeup_task);
+	wakeup_task = get_task_struct(p);
 
 	local_save_flags(flags);