diff options
author | Oleg Nesterov <oleg@redhat.com> | 2010-03-15 10:10:27 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2010-04-02 20:12:03 +0200 |
commit | 9084bb8246ea935b98320554229e2f371f7f52fa (patch) | |
tree | 8478d18125e3b4a7e0a31d702647dee1830d23ef | |
parent | 6a1bdc1b577ebcb65f6603c57f8347309bc4ab13 (diff) | |
download | linux-9084bb8246ea935b98320554229e2f371f7f52fa.tar.bz2 |
sched: Make select_fallback_rq() cpuset friendly
Introduce cpuset_cpus_allowed_fallback() helper to fix the cpuset problems
with select_fallback_rq(). It can be called from any context and can't use
any cpuset locks including task_lock(). It is called when the task doesn't
have online cpus in ->cpus_allowed but ttwu/etc must be able to find a
suitable cpu.
I am not proud of this patch. Everything which needs such a fat comment
can't be good even if correct. But I'd prefer to not change the locking
rules in the code I hardly understand, and in any case I believe this
simple change make the code much more correct compared to deadlocks we
currently have.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091027.GA9155@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r-- | include/linux/cpuset.h | 7 | ||||
-rw-r--r-- | kernel/cpuset.c | 42 | ||||
-rw-r--r-- | kernel/sched.c | 4 |
3 files changed, 50 insertions, 3 deletions
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index eeaaee746bee..a73454aec333 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -21,6 +21,7 @@ extern int number_of_cpusets; /* How many cpusets are defined in system? */ extern int cpuset_init(void); extern void cpuset_init_smp(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); +extern int cpuset_cpus_allowed_fallback(struct task_struct *p); extern nodemask_t cpuset_mems_allowed(struct task_struct *p); #define cpuset_current_mems_allowed (current->mems_allowed) void cpuset_init_current_mems_allowed(void); @@ -101,6 +102,12 @@ static inline void cpuset_cpus_allowed(struct task_struct *p, cpumask_copy(mask, cpu_possible_mask); } +static inline int cpuset_cpus_allowed_fallback(struct task_struct *p) +{ + cpumask_copy(&p->cpus_allowed, cpu_possible_mask); + return cpumask_any(cpu_active_mask); +} + static inline nodemask_t cpuset_mems_allowed(struct task_struct *p) { return node_possible_map; diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 9a747f56d58c..9a50c5f6e727 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -2188,6 +2188,48 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) mutex_unlock(&callback_mutex); } +int cpuset_cpus_allowed_fallback(struct task_struct *tsk) +{ + const struct cpuset *cs; + int cpu; + + rcu_read_lock(); + cs = task_cs(tsk); + if (cs) + cpumask_copy(&tsk->cpus_allowed, cs->cpus_allowed); + rcu_read_unlock(); + + /* + * We own tsk->cpus_allowed, nobody can change it under us. + * + * But we used cs && cs->cpus_allowed lockless and thus can + * race with cgroup_attach_task() or update_cpumask() and get + * the wrong tsk->cpus_allowed. However, both cases imply the + * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr() + * which takes task_rq_lock(). + * + * If we are called after it dropped the lock we must see all + * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary + * set any mask even if it is not right from task_cs() pov, + * the pending set_cpus_allowed_ptr() will fix things. + */ + + cpu = cpumask_any_and(&tsk->cpus_allowed, cpu_active_mask); + if (cpu >= nr_cpu_ids) { + /* + * Either tsk->cpus_allowed is wrong (see above) or it + * is actually empty. The latter case is only possible + * if we are racing with remove_tasks_in_empty_cpuset(). + * Like above we can temporary set any mask and rely on + * set_cpus_allowed_ptr() as synchronization point. + */ + cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask); + cpu = cpumask_any(cpu_active_mask); + } + + return cpu; +} + void cpuset_init_current_mems_allowed(void) { nodes_setall(current->mems_allowed); diff --git a/kernel/sched.c b/kernel/sched.c index 11119deffa48..9a38c7a24ed7 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2300,9 +2300,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p) /* No more Mr. Nice Guy. */ if (unlikely(dest_cpu >= nr_cpu_ids)) { - cpumask_copy(&p->cpus_allowed, cpu_possible_mask); - dest_cpu = cpumask_any(cpu_active_mask); - + dest_cpu = cpuset_cpus_allowed_fallback(p); /* * Don't tell them about moving exiting tasks or * kernel threads (both mm NULL), since they never |