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-rw-r--r--debian/patches-rt/0290-sched-Simplify-migration_cpu_stop.patch142
1 files changed, 142 insertions, 0 deletions
diff --git a/debian/patches-rt/0290-sched-Simplify-migration_cpu_stop.patch b/debian/patches-rt/0290-sched-Simplify-migration_cpu_stop.patch
new file mode 100644
index 000000000..4d0841707
--- /dev/null
+++ b/debian/patches-rt/0290-sched-Simplify-migration_cpu_stop.patch
@@ -0,0 +1,142 @@
+From 4f468832c2a5bb5c0bb23b453038ff4fed722061 Mon Sep 17 00:00:00 2001
+From: Peter Zijlstra <peterz@infradead.org>
+Date: Tue, 8 Jun 2021 00:37:31 -0400
+Subject: [PATCH 290/323] sched: Simplify migration_cpu_stop()
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+commit c20cf065d4a619d394d23290093b1002e27dff86 upstream.
+
+When affine_move_task() issues a migration_cpu_stop(), the purpose of
+that function is to complete that @pending, not any random other
+p->migration_pending that might have gotten installed since.
+
+This realization much simplifies migration_cpu_stop() and allows
+further necessary steps to fix all this as it provides the guarantee
+that @pending's stopper will complete @pending (and not some random
+other @pending).
+
+Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
+Cc: stable@kernel.org
+Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
+Signed-off-by: Ingo Molnar <mingo@kernel.org>
+Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
+Link: https://lkml.kernel.org/r/20210224131355.430014682@infradead.org
+Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
+Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
+---
+ kernel/sched/core.c | 56 +++++++--------------------------------------
+ 1 file changed, 8 insertions(+), 48 deletions(-)
+
+diff --git a/kernel/sched/core.c b/kernel/sched/core.c
+index df9c4c3838c0..31fa925852e5 100644
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -1950,8 +1950,8 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
+ */
+ static int migration_cpu_stop(void *data)
+ {
+- struct set_affinity_pending *pending;
+ struct migration_arg *arg = data;
++ struct set_affinity_pending *pending = arg->pending;
+ struct task_struct *p = arg->task;
+ int dest_cpu = arg->dest_cpu;
+ struct rq *rq = this_rq();
+@@ -1973,25 +1973,6 @@ static int migration_cpu_stop(void *data)
+ raw_spin_lock(&p->pi_lock);
+ rq_lock(rq, &rf);
+
+- pending = p->migration_pending;
+- if (pending && !arg->pending) {
+- /*
+- * This happens from sched_exec() and migrate_task_to(),
+- * neither of them care about pending and just want a task to
+- * maybe move about.
+- *
+- * Even if there is a pending, we can ignore it, since
+- * affine_move_task() will have it's own stop_work's in flight
+- * which will manage the completion.
+- *
+- * Notably, pending doesn't need to match arg->pending. This can
+- * happen when tripple concurrent affine_move_task() first sets
+- * pending, then clears pending and eventually sets another
+- * pending.
+- */
+- pending = NULL;
+- }
+-
+ /*
+ * If task_rq(p) != rq, it cannot be migrated here, because we're
+ * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
+@@ -2002,31 +1983,20 @@ static int migration_cpu_stop(void *data)
+ goto out;
+
+ if (pending) {
+- p->migration_pending = NULL;
++ if (p->migration_pending == pending)
++ p->migration_pending = NULL;
+ complete = true;
+ }
+
+- /* migrate_enable() -- we must not race against SCA */
+- if (dest_cpu < 0) {
+- /*
+- * When this was migrate_enable() but we no longer
+- * have a @pending, a concurrent SCA 'fixed' things
+- * and we should be valid again. Nothing to do.
+- */
+- if (!pending) {
+- WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask));
+- goto out;
+- }
+-
++ if (dest_cpu < 0)
+ dest_cpu = cpumask_any_distribute(&p->cpus_mask);
+- }
+
+ if (task_on_rq_queued(p))
+ rq = __migrate_task(rq, &rf, p, dest_cpu);
+ else
+ p->wake_cpu = dest_cpu;
+
+- } else if (dest_cpu < 0 || pending) {
++ } else if (pending) {
+ /*
+ * This happens when we get migrated between migrate_enable()'s
+ * preempt_enable() and scheduling the stopper task. At that
+@@ -2041,22 +2011,13 @@ static int migration_cpu_stop(void *data)
+ * ->pi_lock, so the allowed mask is stable - if it got
+ * somewhere allowed, we're done.
+ */
+- if (pending && cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
+- p->migration_pending = NULL;
++ if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
++ if (p->migration_pending == pending)
++ p->migration_pending = NULL;
+ complete = true;
+ goto out;
+ }
+
+- /*
+- * When this was migrate_enable() but we no longer have an
+- * @pending, a concurrent SCA 'fixed' things and we should be
+- * valid again. Nothing to do.
+- */
+- if (!pending) {
+- WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask));
+- goto out;
+- }
+-
+ /*
+ * When migrate_enable() hits a rq mis-match we can't reliably
+ * determine is_migration_disabled() and so have to chase after
+@@ -2074,7 +2035,6 @@ static int migration_cpu_stop(void *data)
+ complete_all(&pending->done);
+
+ /* For pending->{arg,stop_work} */
+- pending = arg->pending;
+ if (pending && refcount_dec_and_test(&pending->refs))
+ wake_up_var(&pending->refs);
+
+--
+2.43.0
+