linux-kernel - Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

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Message-ID: <YaFaoQsIBUmq1S/q@hirez.programming.kicks-ass.net>
Date:   Fri, 26 Nov 2021 23:07:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Oskolkov <posk@...k.io>, Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, Paul Turner <pjt@...gle.com>,
        Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Andrei Vagin <avagin@...gle.com>, Jann Horn <jannh@...gle.com>,
        Thierry Delisle <tdelisle@...terloo.ca>
Subject: Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

On Fri, Nov 26, 2021 at 10:59:44PM +0100, Peter Zijlstra wrote:

> That seems to loose the freezable crud.. then again, since we're
> interruptible, that shouldn't matter. Lemme go do that.


---

--- a/kernel/sched/umcg.c
+++ b/kernel/sched/umcg.c
@@ -52,7 +52,7 @@ static int umcg_pin_pages(void)
 
 	server = umcg_get_task(server_tid);
 	if (!server)
-		return -EINVAL;
+		return -ESRCH;
 
 	if (pin_user_pages_fast((unsigned long)self, 1, 0,
 				&tsk->umcg_worker_page) != 1)
@@ -358,18 +358,10 @@ int umcg_wait(u64 timo)
 {
 	struct task_struct *tsk = current;
 	struct umcg_task __user *self = tsk->umcg_task;
-	struct hrtimer_sleeper timeout;
 	struct page *page = NULL;
 	u32 state;
 	int ret;
 
-	if (timo) {
-		hrtimer_init_sleeper_on_stack(&timeout, tsk->umcg_clock,
-					      HRTIMER_MODE_ABS);
-		hrtimer_set_expires_range_ns(&timeout.timer, (s64)timo,
-					     tsk->timer_slack_ns);
-	}
-
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
 
@@ -415,22 +407,16 @@ int umcg_wait(u64 timo)
 			break;
 		}
 
-		if (timo)
-			hrtimer_sleeper_start_expires(&timeout, HRTIMER_MODE_ABS);
-
-		freezable_schedule();
-
-		ret = -ETIMEDOUT;
-		if (timo && !timeout.task)
+		if (!schedule_hrtimeout_range_clock(timo ? &timo : NULL,
+						    tsk->timer_slack_ns,
+						    HRTIMER_MODE_ABS,
+						    tsk->umcg_clock)) {
+			ret = -ETIMEDOUT;
 			break;
+		}
 	}
 	__set_current_state(TASK_RUNNING);
 
-	if (timo) {
-		hrtimer_cancel(&timeout.timer);
-		destroy_hrtimer_on_stack(&timeout.timer);
-	}
-
 	return ret;
 }
 
@@ -515,7 +501,8 @@ void umcg_notify_resume(struct pt_regs *
 		goto done;
 
 	if (state & UMCG_TF_PREEMPT) {
-		umcg_pin_pages();
+		if (umcg_pin_pages())
+			goto die;
 
 		if (umcg_update_state(tsk, UMCG_TASK_RUNNING,
 				      UMCG_TASK_RUNNABLE, &next_tid))
@@ -586,7 +573,9 @@ SYSCALL_DEFINE2(umcg_wait, u32, flags, u
 		tsk->flags &= ~PF_UMCG_WORKER;
 
 	/* see umcg_sys_{enter,exit}() */
-	umcg_pin_pages();
+	ret = umcg_pin_pages();
+	if (ret)
+		return ret;
 
 	ret = umcg_update_state(tsk, UMCG_TASK_RUNNING, UMCG_TASK_RUNNABLE, &next_tid);
 	if (ret)