diff options
Diffstat (limited to 'debian/patches-rt/0295-sched-Don-t-defer-CPU-pick-to-migration_cpu_stop.patch')
| -rw-r--r-- | debian/patches-rt/0295-sched-Don-t-defer-CPU-pick-to-migration_cpu_stop.patch | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/debian/patches-rt/0295-sched-Don-t-defer-CPU-pick-to-migration_cpu_stop.patch b/debian/patches-rt/0295-sched-Don-t-defer-CPU-pick-to-migration_cpu_stop.patch new file mode 100644 index 000000000..e05440c01 --- /dev/null +++ b/debian/patches-rt/0295-sched-Don-t-defer-CPU-pick-to-migration_cpu_stop.patch @@ -0,0 +1,100 @@ +From b625852d41e17fb13b4caf7192734866534d9799 Mon Sep 17 00:00:00 2001 +From: Valentin Schneider <valentin.schneider@arm.com> +Date: Tue, 8 Jun 2021 00:37:36 -0400 +Subject: [PATCH 295/323] sched: Don't defer CPU pick to migration_cpu_stop() +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +commit 475ea6c60279e9f2ddf7e4cf2648cd8ae0608361 upstream. + +Will reported that the 'XXX __migrate_task() can fail' in migration_cpu_stop() +can happen, and it *is* sort of a big deal. Looking at it some more, one +will note there is a glaring hole in the deferred CPU selection: + + (w/ CONFIG_CPUSET=n, so that the affinity mask passed via taskset doesn't + get AND'd with cpu_online_mask) + + $ taskset -pc 0-2 $PID + # offline CPUs 3-4 + $ taskset -pc 3-5 $PID + `\ + $PID may stay on 0-2 due to the cpumask_any_distribute() picking an + offline CPU and __migrate_task() refusing to do anything due to + cpu_is_allowed(). + +set_cpus_allowed_ptr() goes to some length to pick a dest_cpu that matches +the right constraints vs affinity and the online/active state of the +CPUs. Reuse that instead of discarding it in the affine_move_task() case. + +Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") +Reported-by: Will Deacon <will@kernel.org> +Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> +Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> +Link: https://lkml.kernel.org/r/20210526205751.842360-2-valentin.schneider@arm.com +Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> +Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> +--- + kernel/sched/core.c | 20 ++++++++++++-------- + 1 file changed, 12 insertions(+), 8 deletions(-) + +diff --git a/kernel/sched/core.c b/kernel/sched/core.c +index d3b9d69171a2..81b342d6629b 100644 +--- a/kernel/sched/core.c ++++ b/kernel/sched/core.c +@@ -1958,7 +1958,6 @@ static int migration_cpu_stop(void *data) + 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(); + bool complete = false; + struct rq_flags rf; +@@ -1991,19 +1990,15 @@ static int migration_cpu_stop(void *data) + if (p->migration_pending == pending) + p->migration_pending = NULL; + complete = true; +- } + +- if (dest_cpu < 0) { + if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) + goto out; +- +- dest_cpu = cpumask_any_distribute(&p->cpus_mask); + } + + if (task_on_rq_queued(p)) +- rq = __migrate_task(rq, &rf, p, dest_cpu); ++ rq = __migrate_task(rq, &rf, p, arg->dest_cpu); + else +- p->wake_cpu = dest_cpu; ++ p->wake_cpu = arg->dest_cpu; + + /* + * XXX __migrate_task() can fail, at which point we might end +@@ -2282,7 +2277,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag + init_completion(&my_pending.done); + my_pending.arg = (struct migration_arg) { + .task = p, +- .dest_cpu = -1, /* any */ ++ .dest_cpu = dest_cpu, + .pending = &my_pending, + }; + +@@ -2290,6 +2285,15 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag + } else { + pending = p->migration_pending; + refcount_inc(&pending->refs); ++ /* ++ * Affinity has changed, but we've already installed a ++ * pending. migration_cpu_stop() *must* see this, else ++ * we risk a completion of the pending despite having a ++ * task on a disallowed CPU. ++ * ++ * Serialized by p->pi_lock, so this is safe. ++ */ ++ pending->arg.dest_cpu = dest_cpu; + } + } + pending = p->migration_pending; +-- +2.43.0 + |