On Wed, May 29, 2019 at 08:36:45PM +0000, Vineeth Remanan Pillai wrote: > From: Peter Zijlstra <[email protected]> > > 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. It would be cool if the commit comment would explain what the change is going to do about pick_next_task being unsuitable for remote task selection.
> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Signed-off-by: Vineeth Remanan Pillai <[email protected]> > Signed-off-by: Julien Desfossez <[email protected]> > --- > > Chnages in v3 > ------------- > - Minor refactor to remove redundant NULL checks > > Changes in v2 > ------------- > - Fixes a NULL pointer dereference crash > - Subhra Mazumdar > - Tim Chen > > --- > kernel/sched/deadline.c | 21 ++++++++++++++++----- > kernel/sched/fair.c | 36 +++++++++++++++++++++++++++++++++--- > kernel/sched/idle.c | 10 +++++++++- > kernel/sched/rt.c | 21 ++++++++++++++++----- > kernel/sched/sched.h | 2 ++ > kernel/sched/stop_task.c | 21 ++++++++++++++++----- > 6 files changed, 92 insertions(+), 19 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index d3904168857a..64fc444f44f9 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1722,15 +1722,12 @@ 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, struct task_struct *prev, struct rq_flags > *rf) > +static struct task_struct *pick_task_dl(struct rq *rq) > { > struct sched_dl_entity *dl_se; > struct task_struct *p; > struct dl_rq *dl_rq; > > - WARN_ON_ONCE(prev || rf); > - > dl_rq = &rq->dl; > > if (unlikely(!dl_rq->dl_nr_running)) > @@ -1741,7 +1738,19 @@ pick_next_task_dl(struct rq *rq, struct task_struct > *prev, struct rq_flags *rf) > > p = dl_task_of(dl_se); > > - set_next_task_dl(rq, p); > + return p; > +} > + > +static struct task_struct * > +pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > +{ > + struct task_struct *p; > + > + WARN_ON_ONCE(prev || rf); What is an admin to do with this warnding if it shows up in there logs? maybe include some text here to help folks that might hit this warn_on. > + > + p = pick_task_dl(rq); > + if (p) > + set_next_task_dl(rq, p); > > return p; > } > @@ -2388,6 +2397,8 @@ const struct sched_class dl_sched_class = { > .set_next_task = set_next_task_dl, > > #ifdef CONFIG_SMP > + .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 e65f2dfda77a..02e5dfb85e7d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4136,7 +4136,7 @@ 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) { > @@ -4154,13 +4154,13 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct > sched_entity *curr) > /* > * Prefer last buddy, try to return the CPU to a preempted task. > */ > - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) > + if (left && cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < > 1) > se = cfs_rq->last; > > /* > * Someone really wants this to run. If it's not unfair, run it. > */ > - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) > + if (left && cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < > 1) > se = cfs_rq->next; > > clear_buddies(cfs_rq, se); > @@ -6966,6 +6966,34 @@ static void check_preempt_wakeup(struct rq *rq, struct > task_struct *p, int wake_ > set_last_buddy(se); > } > > +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); > +} > + > static struct task_struct * > pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > { > @@ -10677,6 +10705,8 @@ const struct sched_class fair_sched_class = { > .set_next_task = set_next_task_fair, > > #ifdef CONFIG_SMP > + .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 7ece8e820b5d..e7f38da60373 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -373,6 +373,12 @@ static void check_preempt_curr_idle(struct rq *rq, > struct task_struct *p, int fl > resched_curr(rq); > } > > +static struct task_struct * > +pick_task_idle(struct rq *rq) > +{ > + return rq->idle; > +} > + > static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, > struct rq_flags *rf) > { > } > @@ -386,11 +392,12 @@ static void set_next_task_idle(struct rq *rq, struct > task_struct *next) > static struct task_struct * > pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > { > - struct task_struct *next = rq->idle; > + struct task_struct *next; > > if (prev) > put_prev_task(rq, prev); > > + next = pick_task_idle(rq); > set_next_task_idle(rq, next); > > return next; > @@ -458,6 +465,7 @@ const struct sched_class idle_sched_class = { > .set_next_task = set_next_task_idle, > > #ifdef CONFIG_SMP > + .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 79f2e60516ef..81557224548c 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1548,20 +1548,29 @@ 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, struct task_struct *prev, struct rq_flags > *rf) > +static struct task_struct *pick_task_rt(struct rq *rq) > { > struct task_struct *p; > struct rt_rq *rt_rq = &rq->rt; > > - WARN_ON_ONCE(prev || rf); > - > if (!rt_rq->rt_queued) > return NULL; > > p = _pick_next_task_rt(rq); > > - set_next_task_rt(rq, p); > + return p; > +} > + > +static struct task_struct * > +pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > +{ > + struct task_struct *p; > + > + WARN_ON_ONCE(prev || rf); what does it mean if this warn on goes off to an admin? > + > + p = pick_task_rt(rq); > + if (p) > + set_next_task_rt(rq, p); > > return p; > } > @@ -2364,6 +2373,8 @@ const struct sched_class rt_sched_class = { > .set_next_task = set_next_task_rt, > > #ifdef CONFIG_SMP > + .pick_task = pick_task_rt, > + > .select_task_rq = select_task_rq_rt, > > .set_cpus_allowed = set_cpus_allowed_common, > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 460dd04e76af..a024dd80eeb3 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1682,6 +1682,8 @@ struct sched_class { > void (*set_next_task)(struct rq *rq, struct task_struct *p); > > #ifdef CONFIG_SMP > + 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 7e1cee4e65b2..fb6c436cba6c 100644 > --- a/kernel/sched/stop_task.c > +++ b/kernel/sched/stop_task.c > @@ -29,20 +29,30 @@ static void set_next_task_stop(struct rq *rq, struct > task_struct *stop) > } > > static struct task_struct * > -pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > +pick_task_stop(struct rq *rq) > { > struct task_struct *stop = rq->stop; > > - WARN_ON_ONCE(prev || rf); > - > if (!stop || !task_on_rq_queued(stop)) > return NULL; > > - set_next_task_stop(rq, stop); > - > return stop; > } > > +static struct task_struct * > +pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags > *rf) > +{ > + struct task_struct *p; > + > + WARN_ON_ONCE(prev || rf); > + > + p = pick_task_stop(rq); > + if (p) > + set_next_task_stop(rq, p); > + > + return p; > +} > + > static void > enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) > { > @@ -129,6 +139,7 @@ const struct sched_class stop_sched_class = { > .set_next_task = set_next_task_stop, > > #ifdef CONFIG_SMP > + .pick_task = pick_task_stop, > .select_task_rq = select_task_rq_stop, > .set_cpus_allowed = set_cpus_allowed_common, > #endif > -- > 2.17.1 >
