87 lines
3.1 KiB
Diff
87 lines
3.1 KiB
Diff
From cee66e3557735609a551656c2bda190fa2470207 Mon Sep 17 00:00:00 2001
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Message-Id: <cee66e3557735609a551656c2bda190fa2470207.1601675153.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Scott Wood <swood@redhat.com>
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Date: Fri, 24 Jan 2020 06:11:46 -0500
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Subject: [PATCH 316/333] sched: migrate_enable: Use per-cpu cpu_stop_work
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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[ Upstream commit 2dcd94b443c5dcbc20281666321b7f025f9cc85c ]
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Commit e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()")
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adds a busy wait to deal with an edge case where the migrated thread
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can resume running on another CPU before the stopper has consumed
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cpu_stop_work. However, this is done with preemption disabled and can
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potentially lead to deadlock.
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While it is not guaranteed that the cpu_stop_work will be consumed before
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the migrating thread resumes and exits the stack frame, it is guaranteed
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that nothing other than the stopper can run on the old cpu between the
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migrating thread scheduling out and the cpu_stop_work being consumed.
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Thus, we can store cpu_stop_work in per-cpu data without it being
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reused too early.
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Fixes: e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()")
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Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Scott Wood <swood@redhat.com>
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Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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---
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kernel/sched/core.c | 22 ++++++++++++++--------
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1 file changed, 14 insertions(+), 8 deletions(-)
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diff --git a/kernel/sched/core.c b/kernel/sched/core.c
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index ab34c573b79c..098e88f7a216 100644
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -7286,6 +7286,9 @@ static void migrate_disabled_sched(struct task_struct *p)
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p->migrate_disable_scheduled = 1;
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}
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+static DEFINE_PER_CPU(struct cpu_stop_work, migrate_work);
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+static DEFINE_PER_CPU(struct migration_arg, migrate_arg);
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+
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void migrate_enable(void)
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{
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struct task_struct *p = current;
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@@ -7324,23 +7327,26 @@ void migrate_enable(void)
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WARN_ON(smp_processor_id() != cpu);
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if (!is_cpu_allowed(p, cpu)) {
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- struct migration_arg arg = { .task = p };
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- struct cpu_stop_work work;
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+ struct migration_arg __percpu *arg;
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+ struct cpu_stop_work __percpu *work;
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struct rq_flags rf;
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+ work = this_cpu_ptr(&migrate_work);
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+ arg = this_cpu_ptr(&migrate_arg);
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+ WARN_ON_ONCE(!arg->done && !work->disabled && work->arg);
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+
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+ arg->task = p;
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+ arg->done = false;
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+
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rq = task_rq_lock(p, &rf);
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update_rq_clock(rq);
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- arg.dest_cpu = select_fallback_rq(cpu, p);
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+ arg->dest_cpu = select_fallback_rq(cpu, p);
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task_rq_unlock(rq, p, &rf);
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stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
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- &arg, &work);
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+ arg, work);
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tlb_migrate_finish(p->mm);
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__schedule(true);
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- if (!work.disabled) {
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- while (!arg.done)
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- cpu_relax();
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- }
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}
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out:
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--
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2.17.1
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