Linux-rt-users archive on lore.kernel.org
 help / color / Atom feed
From: Scott Wood <swood@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Waiman Long <longman@redhat.com>,
	linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	Scott Wood <swood@redhat.com>
Subject: [PATCH RT v2 1/3] sched: migrate_enable: Use select_fallback_rq()
Date: Sat, 12 Oct 2019 01:52:12 -0500
Message-ID: <20191012065214.28109-2-swood@redhat.com> (raw)
In-Reply-To: <20191012065214.28109-1-swood@redhat.com>

migrate_enable() currently open-codes a variant of select_fallback_rq().
However, it does not have the "No more Mr. Nice Guy" fallback and thus
it will pass an invalid CPU to the migration thread if cpus_mask only
contains a CPU that is !active.

Signed-off-by: Scott Wood <swood@redhat.com>
---
This scenario will be more likely after the next patch, since
the migrate_disable_update check goes away.  However, it could happen
anyway if cpus_mask was updated to a CPU other than the one we were
pinned to, and that CPU subsequently became inactive.
---
 kernel/sched/core.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 93b4ae1ecaff..bfd160e90797 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7405,6 +7405,7 @@ void migrate_enable(void)
 	if (p->migrate_disable_update) {
 		struct rq *rq;
 		struct rq_flags rf;
+		int cpu = task_cpu(p);
 
 		rq = task_rq_lock(p, &rf);
 		update_rq_clock(rq);
@@ -7414,21 +7415,15 @@ void migrate_enable(void)
 
 		p->migrate_disable_update = 0;
 
-		WARN_ON(smp_processor_id() != task_cpu(p));
-		if (!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
-			const struct cpumask *cpu_valid_mask = cpu_active_mask;
-			struct migration_arg arg;
-			unsigned int dest_cpu;
-
-			if (p->flags & PF_KTHREAD) {
-				/*
-				 * Kernel threads are allowed on online && !active CPUs
-				 */
-				cpu_valid_mask = cpu_online_mask;
-			}
-			dest_cpu = cpumask_any_and(cpu_valid_mask, &p->cpus_mask);
-			arg.task = p;
-			arg.dest_cpu = dest_cpu;
+		WARN_ON(smp_processor_id() != cpu);
+		if (!cpumask_test_cpu(cpu, &p->cpus_mask)) {
+			struct migration_arg arg = { p };
+			struct rq_flags rf;
+
+			rq = task_rq_lock(p, &rf);
+			update_rq_clock(rq);
+			arg.dest_cpu = select_fallback_rq(cpu, p);
+			task_rq_unlock(rq, p, &rf);
 
 			unpin_current_cpu();
 			preempt_lazy_enable();
-- 
1.8.3.1


  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-12  6:52 [PATCH RT v2 0/3] migrate disable fixes and performance Scott Wood
2019-10-12  6:52 ` Scott Wood [this message]
2019-10-12  6:52 ` [PATCH RT v2 2/3] sched: Lazy migrate_disable processing Scott Wood
2019-10-18 18:12   ` Waiman Long
2019-10-18 22:11     ` Scott Wood
2019-10-12  6:52 ` [PATCH RT v2 3/3] sched: migrate_enable: Use stop_one_cpu_nowait() Scott Wood
2019-10-18 11:00 ` [PATCH RT v2 0/3] migrate disable fixes and performance Sebastian Andrzej Siewior

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191012065214.28109-2-swood@redhat.com \
    --to=swood@redhat.com \
    --cc=bigeasy@linutronix.de \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=longman@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-rt-users archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rt-users/0 linux-rt-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rt-users linux-rt-users/ https://lore.kernel.org/linux-rt-users \
		linux-rt-users@vger.kernel.org
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rt-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git