linux-kernel - [PATCH 3/8] sched: Simplify sched

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Message-ID: <20230809204200.241599953@infradead.org>
Date:   Wed, 09 Aug 2023 22:24:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...hat.com
Cc:     peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/8] sched: Simplify sched_{set,get}affinity()

Use guards to reduce gotos and simplify control flow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/core.c |   53 +++++++++++++---------------------------------------
 1 file changed, 14 insertions(+), 39 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8258,39 +8258,24 @@ long sched_setaffinity(pid_t pid, const
 {
 	struct affinity_context ac;
 	struct cpumask *user_mask;
-	struct task_struct *p;
 	int retval;
 
-	rcu_read_lock();
-
-	p = find_process_by_pid(pid);
-	if (!p) {
-		rcu_read_unlock();
+	CLASS(find_get_task, p)(pid);
+	if (!p)
 		return -ESRCH;
-	}
 
-	/* Prevent p going away */
-	get_task_struct(p);
-	rcu_read_unlock();
-
-	if (p->flags & PF_NO_SETAFFINITY) {
-		retval = -EINVAL;
-		goto out_put_task;
-	}
+	if (p->flags & PF_NO_SETAFFINITY)
+		return -EINVAL;
 
 	if (!check_same_owner(p)) {
-		rcu_read_lock();
-		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
-			rcu_read_unlock();
-			retval = -EPERM;
-			goto out_put_task;
-		}
-		rcu_read_unlock();
+		guard(rcu)();
+		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
+			return -EPERM;
 	}
 
 	retval = security_task_setscheduler(p);
 	if (retval)
-		goto out_put_task;
+		return retval;
 
 	/*
 	 * With non-SMP configs, user_cpus_ptr/user_mask isn't used and
@@ -8300,8 +8285,7 @@ long sched_setaffinity(pid_t pid, const
 	if (user_mask) {
 		cpumask_copy(user_mask, in_mask);
 	} else if (IS_ENABLED(CONFIG_SMP)) {
-		retval = -ENOMEM;
-		goto out_put_task;
+		return -ENOMEM;
 	}
 
 	ac = (struct affinity_context){
@@ -8313,8 +8297,6 @@ long sched_setaffinity(pid_t pid, const
 	retval = __sched_setaffinity(p, &ac);
 	kfree(ac.user_mask);
 
-out_put_task:
-	put_task_struct(p);
 	return retval;
 }
 
@@ -8356,28 +8338,21 @@ SYSCALL_DEFINE3(sched_setaffinity, pid_t
 long sched_getaffinity(pid_t pid, struct cpumask *mask)
 {
 	struct task_struct *p;
-	unsigned long flags;
 	int retval;
 
-	rcu_read_lock();
-
-	retval = -ESRCH;
+	guard(rcu)();
 	p = find_process_by_pid(pid);
 	if (!p)
-		goto out_unlock;
+		return -ESRCH;
 
 	retval = security_task_getscheduler(p);
 	if (retval)
-		goto out_unlock;
+		return retval;
 
-	raw_spin_lock_irqsave(&p->pi_lock, flags);
+	guard(raw_spinlock_irqsave)(&p->pi_lock);
 	cpumask_and(mask, &p->cpus_mask, cpu_active_mask);
-	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
-out_unlock:
-	rcu_read_unlock();
-
-	return retval;
+	return 0;
 }
 
 /**