lkml.org 
[lkml]   [2010]   [Dec]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH] avoid race condition in pick_next_task_fair in kernel/sched_fair.c
From
Date
On Thu, 2010-12-23 at 13:33 +0100, Peter Zijlstra wrote:

> systemd-1 0d..1. 2070793us : sched_destroy_group: se: f69e43c0, load: 1024
> systemd-1 0d..1. 2070794us : sched_destroy_group: cfs_rq: f69e4720, nr: 1, load: 1024
> systemd-1 0d..1. 2070794us : __print_runqueue: cfs_rq: f69e4720, nr: 1, load: 1024
> systemd-1 0d..1. 2070795us : __print_runqueue: curr: (null)
> systemd-1 0d..1. 2070796us : __print_runqueue: se: f6a8eb4c, comm: systemd-tmpfile/1243, load: 1024
> systemd-1 0d..1. 2070796us : _raw_spin_unlock_irqrestore <-sched_destroy_group
>
> So somehow it manages to destroy a group with a task attached.

Its even weirder:

systemd-1 0d..1. 1663489us : sched_destroy_group: se: f69e7360, load: 1024
systemd-1 0d..1. 1663489us : sched_destroy_group: cfs_rq: f69e72a0, nr: 1, load: 1024
systemd-1 0d..1. 1663491us : __print_runqueue: cfs_rq: f69e72a0, nr: 1, load: 1024, cgroup: /system/systemd-sysctl.service
systemd-1 0d..1. 1663491us : __print_runqueue: curr: (null)
systemd-1 0d..1. 1663493us : __print_runqueue: se: f69d95bc, comm: systemd-sysctl/1209, load: 1024, cgroup: /
systemd-1 0d..1. 1663496us : do_invalid_op <-error_code

The task enqueued to the cfs_rq doesn't match the cgroup, the thing is,
I don't see a cpu_cgroup_attach/sched_move_task call in the log, nor
does a BUG_ON() validating the task's cgroup against the cfs_rq's cgroup
on account_entity_enqueue() trigger.

So it looks like a task changes cgroup without passing through the
cgroup_subsys::attach method, which afaict isn't supposed to happen.

---
kernel/sched.c | 26 ++++++++++++++-
kernel/sched_fair.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 113 insertions(+), 2 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index dc85ceb..bc30efb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8033,10 +8033,20 @@ static void free_fair_sched_group(struct task_group *tg)
int i;

for_each_possible_cpu(i) {
- if (tg->cfs_rq)
+ if (tg->cfs_rq) {
+ struct cfs_rq *cfs_rq = tg->cfs_rq[i];
+ if (cfs_rq) {
+ trace_printk("cfs_rq: %p, nr: %ld, load: %ld\n",
+ cfs_rq, cfs_rq->nr_running, cfs_rq->load.weight);
+ }
kfree(tg->cfs_rq[i]);
- if (tg->se)
+ }
+ if (tg->se) {
+ struct sched_entity *se = tg->se[i];
+ if (se)
+ trace_printk("se: %p, load: %ld\n", se, se->load.weight);
kfree(tg->se[i]);
+ }
}

kfree(tg->cfs_rq);
@@ -8092,6 +8102,18 @@ static inline void register_fair_sched_group(struct task_group *tg, int cpu)

static inline void unregister_fair_sched_group(struct task_group *tg, int cpu)
{
+ struct cfs_rq *cfs_rq = tg->cfs_rq[cpu];
+ struct sched_entity *se = tg->se[cpu];
+
+ trace_printk("se: %p, load: %ld\n", se, se->load.weight);
+ trace_printk("cfs_rq: %p, nr: %ld, load: %ld\n",
+ cfs_rq, cfs_rq->nr_running, cfs_rq->load.weight);
+
+ if (cfs_rq->nr_running) {
+ print_runqueue(cfs_rq);
+ BUG();
+ }
+
list_del_rcu(&tg->cfs_rq[cpu]->leaf_cfs_rq_list);
}
#else /* !CONFG_FAIR_GROUP_SCHED */
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index db3f674..37d918a 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -333,6 +333,8 @@ static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
s64 key = entity_key(cfs_rq, se);
int leftmost = 1;

+ trace_printk("%p to %p, %ld tasks\n", se, cfs_rq, cfs_rq->nr_running);
+
/*
* Find the right place in the rbtree:
*/
@@ -364,6 +366,8 @@ static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
+ trace_printk("%p from %p, %ld left\n", se, cfs_rq, cfs_rq->nr_running);
+
if (cfs_rq->rb_leftmost == &se->run_node) {
struct rb_node *next_node;

@@ -394,6 +398,70 @@ static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
return rb_entry(last, struct sched_entity, run_node);
}

+#define INDENT(i) ((i)*2), " "
+
+static void notrace __print_runqueue(struct cfs_rq *cfs_rq, int indent);
+
+static __always_inline
+char *task_group_path(struct task_group *tg, char *buf, int buflen)
+{
+ /* may be NULL if the underlying cgroup isn't fully-created yet */
+ if (!tg->css.cgroup)
+ buf[0] = '\0';
+ else
+ cgroup_path(tg->css.cgroup, buf, buflen);
+
+ return buf;
+}
+
+static void __always_inline
+__print_entity(struct sched_entity *se, char *name, int indent)
+{
+ if (!se) {
+ trace_printk("%.*s %s: %p\n", INDENT(indent), name, se);
+ return;
+ }
+
+ if (entity_is_task(se)) {
+ struct task_struct *p = task_of(se);
+ char buf[64];
+
+ trace_printk("%.*s %s: %p, comm: %s/%d, load: %ld, cgroup: %s\n",
+ INDENT(indent), name,
+ se, p->comm, p->pid, se->load.weight,
+ task_group_path(task_group(p), buf, sizeof(buf)));
+ } else {
+ trace_printk("%.*s %s: %p, load: %ld, ",
+ INDENT(indent), name,
+ se, se->load.weight);
+ __print_runqueue(group_cfs_rq(se), indent+1);
+ }
+}
+
+static void notrace __print_runqueue(struct cfs_rq *cfs_rq, int indent)
+{
+ struct rb_node *n;
+ char buf[64];
+
+ trace_printk("%.*s cfs_rq: %p, nr: %ld, load: %ld, cgroup: %s\n",
+ INDENT(indent),
+ cfs_rq, cfs_rq->nr_running,
+ cfs_rq->load.weight,
+ task_group_path(cfs_rq->tg, buf, sizeof(buf)));
+
+ __print_entity(cfs_rq->curr, "curr", indent);
+
+ for (n = cfs_rq->rb_leftmost; n; n = rb_next(n)) {
+ struct sched_entity *se = rb_entry(n, struct sched_entity, run_node);
+ __print_entity(se, "se", indent);
+ }
+}
+
+void notrace print_runqueue(struct cfs_rq *cfs_rq)
+{
+ __print_runqueue(cfs_rq, 0);
+}
+
/**************************************************************
* Scheduling class statistics methods:
*/
@@ -631,6 +699,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
if (entity_is_task(se)) {
add_cfs_task_weight(cfs_rq, se->load.weight);
list_add(&se->group_node, &cfs_rq->tasks);
+ BUG_ON(task_group(task_of(se)) != cfs_rq->tg);
}
cfs_rq->nr_running++;
se->on_rq = 1;
@@ -1047,6 +1116,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se;

+ print_runqueue(&rq->cfs);
for_each_sched_entity(se) {
if (se->on_rq)
break;
@@ -1055,6 +1125,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
flags = ENQUEUE_WAKEUP;
}

+ trace_printk("add task: %p, %s/%d\n", &p->se, p->comm, p->pid);
+ print_runqueue(&rq->cfs);
+
hrtick_update(rq);
}

@@ -1068,6 +1141,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se;

+ print_runqueue(&rq->cfs);
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, flags);
@@ -1077,6 +1151,9 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
flags |= DEQUEUE_SLEEP;
}

+ trace_printk("del task: %p, %s/%d\n", &p->se, p->comm, p->pid);
+ print_runqueue(&rq->cfs);
+
hrtick_update(rq);
}

@@ -1719,6 +1796,8 @@ static struct task_struct *pick_next_task_fair(struct rq *rq)
struct cfs_rq *cfs_rq = &rq->cfs;
struct sched_entity *se;

+ print_runqueue(&rq->cfs);
+
if (!cfs_rq->nr_running)
return NULL;

@@ -1731,6 +1810,9 @@ static struct task_struct *pick_next_task_fair(struct rq *rq)
p = task_of(se);
hrtick_start_fair(rq, p);

+ trace_printk("picked: %p, %s/%d\n", se, p->comm, p->pid);
+ print_runqueue(&rq->cfs);
+
return p;
}

@@ -1742,10 +1824,15 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
struct sched_entity *se = &prev->se;
struct cfs_rq *cfs_rq;

+ print_runqueue(&rq->cfs);
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
put_prev_entity(cfs_rq, se);
}
+
+ trace_printk("put: %p, %s/%d\n", se, prev->comm, prev->pid);
+ print_runqueue(&rq->cfs);
+
}

#ifdef CONFIG_SMP
@@ -3819,8 +3906,10 @@ static void set_curr_task_fair(struct rq *rq)
{
struct sched_entity *se = &rq->curr->se;

+ print_runqueue(&rq->cfs);
for_each_sched_entity(se)
set_next_entity(cfs_rq_of(se), se);
+ print_runqueue(&rq->cfs);
}

#ifdef CONFIG_FAIR_GROUP_SCHED


\
 
 \ /
  Last update: 2010-12-23 19:27    [W:0.420 / U:0.708 seconds]
©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site