diff options
Diffstat (limited to 'debian/patches-rt/0316-sched-migrate_enable-Use-per-cpu-cpu_stop_work.patch')
| -rw-r--r-- | debian/patches-rt/0316-sched-migrate_enable-Use-per-cpu-cpu_stop_work.patch | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/debian/patches-rt/0316-sched-migrate_enable-Use-per-cpu-cpu_stop_work.patch b/debian/patches-rt/0316-sched-migrate_enable-Use-per-cpu-cpu_stop_work.patch new file mode 100644 index 000000000..fcff1b8a4 --- /dev/null +++ b/debian/patches-rt/0316-sched-migrate_enable-Use-per-cpu-cpu_stop_work.patch @@ -0,0 +1,83 @@ +From 5595f7a45953987f56b3e64c3a20f6f90735d4a1 Mon Sep 17 00:00:00 2001 +From: Scott Wood <swood@redhat.com> +Date: Fri, 24 Jan 2020 06:11:46 -0500 +Subject: [PATCH 316/347] sched: migrate_enable: Use per-cpu cpu_stop_work +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz + +[ Upstream commit 2dcd94b443c5dcbc20281666321b7f025f9cc85c ] + +Commit e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()") +adds a busy wait to deal with an edge case where the migrated thread +can resume running on another CPU before the stopper has consumed +cpu_stop_work. However, this is done with preemption disabled and can +potentially lead to deadlock. + +While it is not guaranteed that the cpu_stop_work will be consumed before +the migrating thread resumes and exits the stack frame, it is guaranteed +that nothing other than the stopper can run on the old cpu between the +migrating thread scheduling out and the cpu_stop_work being consumed. +Thus, we can store cpu_stop_work in per-cpu data without it being +reused too early. + +Fixes: e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()") +Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Signed-off-by: Scott Wood <swood@redhat.com> +Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> +--- + kernel/sched/core.c | 22 ++++++++++++++-------- + 1 file changed, 14 insertions(+), 8 deletions(-) + +diff --git a/kernel/sched/core.c b/kernel/sched/core.c +index d190d9e6b10f..8b946353b1d7 100644 +--- a/kernel/sched/core.c ++++ b/kernel/sched/core.c +@@ -7285,6 +7285,9 @@ static void migrate_disabled_sched(struct task_struct *p) + p->migrate_disable_scheduled = 1; + } + ++static DEFINE_PER_CPU(struct cpu_stop_work, migrate_work); ++static DEFINE_PER_CPU(struct migration_arg, migrate_arg); ++ + void migrate_enable(void) + { + struct task_struct *p = current; +@@ -7323,23 +7326,26 @@ void migrate_enable(void) + + WARN_ON(smp_processor_id() != cpu); + if (!is_cpu_allowed(p, cpu)) { +- struct migration_arg arg = { .task = p }; +- struct cpu_stop_work work; ++ struct migration_arg __percpu *arg; ++ struct cpu_stop_work __percpu *work; + struct rq_flags rf; + ++ work = this_cpu_ptr(&migrate_work); ++ arg = this_cpu_ptr(&migrate_arg); ++ WARN_ON_ONCE(!arg->done && !work->disabled && work->arg); ++ ++ arg->task = p; ++ arg->done = false; ++ + rq = task_rq_lock(p, &rf); + update_rq_clock(rq); +- arg.dest_cpu = select_fallback_rq(cpu, p); ++ arg->dest_cpu = select_fallback_rq(cpu, p); + task_rq_unlock(rq, p, &rf); + + stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop, +- &arg, &work); ++ arg, work); + tlb_migrate_finish(p->mm); + __schedule(true); +- if (!work.disabled) { +- while (!arg.done) +- cpu_relax(); +- } + } + + out: +-- +2.36.1 + |