On 2020/10/20 9:43, Joel Fernandes (Google) wrote:
> From: Peter Zijlstra <pet...@infradead.org>
>
> Because sched_class::pick_next_task() also implies
> sched_class::set_next_task() (and possibly put_prev_task() and
> newidle_balance) it is not state invariant. This makes it unsuitable
> for remote task selection.
>
> Tested-by: Julien Desfossez <jdesfos...@digitalocean.com>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> Signed-off-by: Vineeth Remanan Pillai <vpil...@digitalocean.com>
> Signed-off-by: Julien Desfossez <jdesfos...@digitalocean.com>
> Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
> ---
> kernel/sched/deadline.c | 16 ++++++++++++++--
> kernel/sched/fair.c | 32 +++++++++++++++++++++++++++++++-
> kernel/sched/idle.c | 8 ++++++++
> kernel/sched/rt.c | 14 ++++++++++++--
> kernel/sched/sched.h | 3 +++
> kernel/sched/stop_task.c | 13 +++++++++++--
> 6 files changed, 79 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 814ec49502b1..0271a7848ab3 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1848,7 +1848,7 @@ static struct sched_dl_entity
> *pick_next_dl_entity(struct rq *rq,
> return rb_entry(left, struct sched_dl_entity, rb_node);
> }
>
> -static struct task_struct *pick_next_task_dl(struct rq *rq)
> +static struct task_struct *pick_task_dl(struct rq *rq)
> {
> struct sched_dl_entity *dl_se;
> struct dl_rq *dl_rq = &rq->dl;
> @@ -1860,7 +1860,18 @@ static struct task_struct *pick_next_task_dl(struct rq
> *rq)
> dl_se = pick_next_dl_entity(rq, dl_rq);
> BUG_ON(!dl_se);
> p = dl_task_of(dl_se);
> - set_next_task_dl(rq, p, true);
> +
> + return p;
> +}
> +
> +static struct task_struct *pick_next_task_dl(struct rq *rq)
> +{
> + struct task_struct *p;
> +
> + p = pick_task_dl(rq);
> + if (p)
> + set_next_task_dl(rq, p, true);
> +
> return p;
> }
>
> @@ -2517,6 +2528,7 @@ const struct sched_class dl_sched_class
>
> #ifdef CONFIG_SMP
> .balance = balance_dl,
> + .pick_task = pick_task_dl,
> .select_task_rq = select_task_rq_dl,
> .migrate_task_rq = migrate_task_rq_dl,
> .set_cpus_allowed = set_cpus_allowed_dl,
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index dbd9368a959d..bd6aed63f5e3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4450,7 +4450,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct
> sched_entity *curr)
> * Avoid running the skip buddy, if running something else can
> * be done without getting too unfair.
> */
> - if (cfs_rq->skip == se) {
> + if (cfs_rq->skip && cfs_rq->skip == se) {
> struct sched_entity *second;
>
> if (se == curr) {
> @@ -6976,6 +6976,35 @@ static void check_preempt_wakeup(struct rq *rq, struct
> task_struct *p, int wake_
> set_last_buddy(se);
> }
>
> +#ifdef CONFIG_SMP
> +static struct task_struct *pick_task_fair(struct rq *rq)
> +{
> + struct cfs_rq *cfs_rq = &rq->cfs;
> + struct sched_entity *se;
> +
> + if (!cfs_rq->nr_running)
> + return NULL;
> +
> + do {
> + struct sched_entity *curr = cfs_rq->curr;
> +
> + se = pick_next_entity(cfs_rq, NULL);
> +
> + if (curr) {
> + if (se && curr->on_rq)
> + update_curr(cfs_rq);
> +
> + if (!se || entity_before(curr, se))
> + se = curr;
> + }
> +
> + cfs_rq = group_cfs_rq(se);
> + } while (cfs_rq);
> +
> + return task_of(se);
> +}
> +#endif
One of my machines hangs when I run uperf with only one message:
[ 719.034962] BUG: kernel NULL pointer dereference, address: 0000000000000050
Then I replicated the problem on my another machine(no serial console),
here is the stack by manual copy.
Call Trace:
pick_next_entity+0xb0/0x160
pick_task_fair+0x4b/0x90
__schedule+0x59b/0x12f0
schedule_idle+0x1e/0x40
do_idle+0x193/0x2d0
cpu_startup_entry+0x19/0x20
start_secondary+0x110/0x150
secondary_startup_64_no_verify+0xa6/0xab
> +
> struct task_struct *
> pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags
> *rf)
> {
> @@ -11173,6 +11202,7 @@ const struct sched_class fair_sched_class
>
> #ifdef CONFIG_SMP
> .balance = balance_fair,
> + .pick_task = pick_task_fair,
> .select_task_rq = select_task_rq_fair,
> .migrate_task_rq = migrate_task_rq_fair,
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 8ce6e80352cf..ce7552c6bc65 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -405,6 +405,13 @@ static void set_next_task_idle(struct rq *rq, struct
> task_struct *next, bool fir
> schedstat_inc(rq->sched_goidle);
> }
>
> +#ifdef CONFIG_SMP
> +static struct task_struct *pick_task_idle(struct rq *rq)
> +{
> + return rq->idle;
> +}
> +#endif
> +
> struct task_struct *pick_next_task_idle(struct rq *rq)
> {
> struct task_struct *next = rq->idle;
> @@ -472,6 +479,7 @@ const struct sched_class idle_sched_class
>
> #ifdef CONFIG_SMP
> .balance = balance_idle,
> + .pick_task = pick_task_idle,
> .select_task_rq = select_task_rq_idle,
> .set_cpus_allowed = set_cpus_allowed_common,
> #endif
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index e57fca05b660..a5851c775270 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1624,7 +1624,7 @@ static struct task_struct *_pick_next_task_rt(struct rq
> *rq)
> return rt_task_of(rt_se);
> }
>
> -static struct task_struct *pick_next_task_rt(struct rq *rq)
> +static struct task_struct *pick_task_rt(struct rq *rq)
> {
> struct task_struct *p;
>
> @@ -1632,7 +1632,16 @@ static struct task_struct *pick_next_task_rt(struct rq
> *rq)
> return NULL;
>
> p = _pick_next_task_rt(rq);
> - set_next_task_rt(rq, p, true);
> +
> + return p;
> +}
> +
> +static struct task_struct *pick_next_task_rt(struct rq *rq)
> +{
> + struct task_struct *p = pick_task_rt(rq);
> + if (p)
> + set_next_task_rt(rq, p, true);
> +
> return p;
> }
>
> @@ -2443,6 +2452,7 @@ const struct sched_class rt_sched_class
>
> #ifdef CONFIG_SMP
> .balance = balance_rt,
> + .pick_task = pick_task_rt,
> .select_task_rq = select_task_rq_rt,
> .set_cpus_allowed = set_cpus_allowed_common,
> .rq_online = rq_online_rt,
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 587ebabebaff..54bfac702805 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1800,6 +1800,9 @@ struct sched_class {
>
> #ifdef CONFIG_SMP
> int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags
> *rf);
> +
> + struct task_struct * (*pick_task)(struct rq *rq);
> +
> int (*select_task_rq)(struct task_struct *p, int task_cpu, int
> sd_flag, int flags);
> void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
>
> diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> index 394bc8126a1e..8f92915dd95e 100644
> --- a/kernel/sched/stop_task.c
> +++ b/kernel/sched/stop_task.c
> @@ -34,15 +34,23 @@ static void set_next_task_stop(struct rq *rq, struct
> task_struct *stop, bool fir
> stop->se.exec_start = rq_clock_task(rq);
> }
>
> -static struct task_struct *pick_next_task_stop(struct rq *rq)
> +static struct task_struct *pick_task_stop(struct rq *rq)
> {
> if (!sched_stop_runnable(rq))
> return NULL;
>
> - set_next_task_stop(rq, rq->stop, true);
> return rq->stop;
> }
>
> +static struct task_struct *pick_next_task_stop(struct rq *rq)
> +{
> + struct task_struct *p = pick_task_stop(rq);
> + if (p)
> + set_next_task_stop(rq, p, true);
> +
> + return p;
> +}
> +
> static void
> enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
> {
> @@ -124,6 +132,7 @@ const struct sched_class stop_sched_class
>
> #ifdef CONFIG_SMP
> .balance = balance_stop,
> + .pick_task = pick_task_stop,
> .select_task_rq = select_task_rq_stop,
> .set_cpus_allowed = set_cpus_allowed_common,
> #endif
>
