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Red Hat Bugzilla – Attachment 308389 Details for
Bug 449676
Turning a CPU offline causes panic
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[patch]
Proposed fix
sched-fix-cpupri-hotplug-2.patch (text/plain), 7.95 KB, created by
Gregory Haskins
on 2008-06-04 19:43:30 UTC
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Description:
Proposed fix
Filename:
MIME Type:
Creator:
Gregory Haskins
Created:
2008-06-04 19:43:30 UTC
Size:
7.95 KB
patch
obsolete
>sched: fix cpupri hotplug support > >From: Gregory Haskins <ghaskins@novell.com> > >The RT folks over at RedHat found an issue w.r.t. hotplug support which >was traced to problems with the cpupri infrastructure in the scheduler: > >https://bugzilla.redhat.com/show_bug.cgi?id=449676 > >This bug affects 23-rt12+, 24-rtX, 25-rtX, and sched-devel. This patch >applies to 25.4-rt4, though it should trivially apply to most cpupri enabled >kernels mentioned above. > >It turned out that the issue was that offline cpus could get inadvertently >registered with cpupri so that they were erroneously selected during >migration decisions. The end result would be an OOPS as the offline cpu >had tasks routed to it. > >This patch generalizes the old join/leave domain interface into an >online/offline interface, and adjusts the root-domain/hotplug code to >utilize it. > >I was able to easily reproduce the issue prior to this patch, and am no >longer able to reproduce it after this patch. I can offline cpus >indefinately and everything seems to be in working order. > >Thanks to Arnaldo (acme), Thomas, and Peter for doing the legwork to point >me in the right direction. Also thank you to Peter for reviewing the >early iterations of this patch. > >Signed-off-by: Gregory Haskins <ghaskins@novell.com> >CC: Ingo Molnar <mingo@elte.hu> >CC: Thomas Gleixner <tglx@linutonix.de> >CC: Steven Rostedt <rostedt@goodmis.org> >CC: Arnaldo Carvalho de Melo <acme@redhat.com> >CC: Peter Zijlstra <peterz@infradead.org> >--- > > include/linux/sched.h | 4 ++-- > kernel/sched.c | 54 ++++++++++++++++++++++++++++++++++++------------- > kernel/sched_rt.c | 24 ++++++++++++++++------ > 3 files changed, 60 insertions(+), 22 deletions(-) > >diff --git a/include/linux/sched.h b/include/linux/sched.h >index bb71371..3b6fab8 100644 >--- a/include/linux/sched.h >+++ b/include/linux/sched.h >@@ -968,8 +968,8 @@ struct sched_class { > void (*task_new) (struct rq *rq, struct task_struct *p); > void (*set_cpus_allowed)(struct task_struct *p, cpumask_t *newmask); > >- void (*join_domain)(struct rq *rq); >- void (*leave_domain)(struct rq *rq); >+ void (*rq_online)(struct rq *rq); >+ void (*rq_offline)(struct rq *rq); > > void (*switched_from) (struct rq *this_rq, struct task_struct *task, > int running); >diff --git a/kernel/sched.c b/kernel/sched.c >index 0399411..31f91d9 100644 >--- a/kernel/sched.c >+++ b/kernel/sched.c >@@ -489,6 +489,7 @@ struct rq { > int push_cpu; > /* cpu of this runqueue: */ > int cpu; >+ int online; > > struct task_struct *migration_thread; > struct list_head migration_queue; >@@ -1320,6 +1321,8 @@ static int task_hot(struct task_struct *p, u64 now, struct sched_domain *sd); > #endif > > #define sched_class_highest (&rt_sched_class) >+#define for_each_class(class) \ >+ for (class = sched_class_highest; class; class = class->next) > > static inline void inc_load(struct rq *rq, const struct task_struct *p) > { >@@ -6278,6 +6281,36 @@ static void unregister_sched_domain_sysctl(void) > } > #endif > >+static void set_rq_online(struct rq *rq) >+{ >+ if (!rq->online) { >+ const struct sched_class *class; >+ >+ cpu_set(rq->cpu, rq->rd->online); >+ rq->online = 1; >+ >+ for_each_class(class) { >+ if (class->rq_online) >+ class->rq_online(rq); >+ } >+ } >+} >+ >+static void set_rq_offline(struct rq *rq) >+{ >+ if (rq->online) { >+ const struct sched_class *class; >+ >+ for_each_class(class) { >+ if (class->rq_offline) >+ class->rq_offline(rq); >+ } >+ >+ cpu_clear(rq->cpu, rq->rd->online); >+ rq->online = 0; >+ } >+} >+ > /* > * migration_call - callback that gets triggered when a CPU is added. > * Here we can start up the necessary migration thread for the new CPU. >@@ -6315,7 +6348,8 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) > spin_lock_irqsave(&rq->lock, flags); > if (rq->rd) { > BUG_ON(!cpu_isset(cpu, rq->rd->span)); >- cpu_set(cpu, rq->rd->online); >+ >+ set_rq_online(rq); > } > spin_unlock_irqrestore(&rq->lock, flags); > break; >@@ -6376,7 +6410,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) > spin_lock_irqsave(&rq->lock, flags); > if (rq->rd) { > BUG_ON(!cpu_isset(cpu, rq->rd->span)); >- cpu_clear(cpu, rq->rd->online); >+ set_rq_offline(rq); > } > spin_unlock_irqrestore(&rq->lock, flags); > break; >@@ -6571,7 +6605,6 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent) > static void rq_attach_root(struct rq *rq, struct root_domain *rd) > { > unsigned long flags; >- const struct sched_class *class; > struct root_domain *reap = NULL; > > spin_lock_irqsave(&rq->lock, flags); >@@ -6579,13 +6612,10 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd) > if (rq->rd) { > struct root_domain *old_rd = rq->rd; > >- for (class = sched_class_highest; class; class = class->next) { >- if (class->leave_domain) >- class->leave_domain(rq); >- } >+ if (cpu_isset(rq->cpu, old_rd->online)) >+ set_rq_offline(rq); > > cpu_clear(rq->cpu, old_rd->span); >- cpu_clear(rq->cpu, old_rd->online); > > if (atomic_dec_and_test(&old_rd->refcount)) > reap = old_rd; >@@ -6596,12 +6626,7 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd) > > cpu_set(rq->cpu, rd->span); > if (cpu_isset(rq->cpu, cpu_online_map)) >- cpu_set(rq->cpu, rd->online); >- >- for (class = sched_class_highest; class; class = class->next) { >- if (class->join_domain) >- class->join_domain(rq); >- } >+ set_rq_online(rq); > > spin_unlock_irqrestore(&rq->lock, flags); > >@@ -7692,6 +7717,7 @@ void __init sched_init(void) > rq->next_balance = jiffies; > rq->push_cpu = 0; > rq->cpu = i; >+ rq->online = 0; > rq->migration_thread = NULL; > INIT_LIST_HEAD(&rq->migration_queue); > rq_attach_root(rq, &def_root_domain); >diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c >index 425cf01..9f2d200 100644 >--- a/kernel/sched_rt.c >+++ b/kernel/sched_rt.c >@@ -12,6 +12,9 @@ static inline int rt_overloaded(struct rq *rq) > > static inline void rt_set_overload(struct rq *rq) > { >+ if (!rq->online) >+ return; >+ > cpu_set(rq->cpu, rq->rd->rto_mask); > /* > * Make sure the mask is visible before we set >@@ -26,6 +29,9 @@ static inline void rt_set_overload(struct rq *rq) > > static inline void rt_clear_overload(struct rq *rq) > { >+ if (!rq->online) >+ return; >+ > /* the order here really doesn't matter */ > atomic_dec(&rq->rd->rto_count); > cpu_clear(rq->cpu, rq->rd->rto_mask); >@@ -280,7 +286,10 @@ void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) > if (rt_se_prio(rt_se) < rt_rq->highest_prio) { > struct rq *rq = rq_of_rt_rq(rt_rq); > rt_rq->highest_prio = rt_se_prio(rt_se); >- cpupri_set(&rq->rd->cpupri, rq->cpu, rt_se_prio(rt_se)); >+ >+ if (rq->online) >+ cpupri_set(&rq->rd->cpupri, rq->cpu, >+ rt_se_prio(rt_se)); > } > #endif > #ifdef CONFIG_SMP >@@ -330,7 +339,10 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) > > if (rt_rq->highest_prio != highest_prio) { > struct rq *rq = rq_of_rt_rq(rt_rq); >- cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio); >+ >+ if (rq->online) >+ cpupri_set(&rq->rd->cpupri, rq->cpu, >+ rt_rq->highest_prio); > } > > update_rt_migration(rq_of_rt_rq(rt_rq)); >@@ -1101,7 +1113,7 @@ static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask) > } > > /* Assumes rq->lock is held */ >-static void join_domain_rt(struct rq *rq) >+static void rq_online_rt(struct rq *rq) > { > if (rq->rt.overloaded) > rt_set_overload(rq); >@@ -1110,7 +1122,7 @@ static void join_domain_rt(struct rq *rq) > } > > /* Assumes rq->lock is held */ >-static void leave_domain_rt(struct rq *rq) >+static void rq_offline_rt(struct rq *rq) > { > if (rq->rt.overloaded) > rt_clear_overload(rq); >@@ -1278,8 +1290,8 @@ const struct sched_class rt_sched_class = { > .load_balance = load_balance_rt, > .move_one_task = move_one_task_rt, > .set_cpus_allowed = set_cpus_allowed_rt, >- .join_domain = join_domain_rt, >- .leave_domain = leave_domain_rt, >+ .rq_online = rq_online_rt, >+ .rq_offline = rq_offline_rt, > .pre_schedule = pre_schedule_rt, > .post_schedule = post_schedule_rt, > .task_wake_up = task_wake_up_rt,
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308386
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