Messages in this thread | | | Date | Tue, 20 Mar 2012 18:44:34 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] Fix the race between smp_call_function and CPU booting |
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[ Adding a few more Cc's since this affects suspend/resume. ]
On 03/20/2012 05:47 PM, Peter Zijlstra wrote:
> On Tue, 2012-03-20 at 00:22 +0000, Liu, Chuansheng wrote: >> Thanks to give some time to have a look. >> > Does the below on top of current tip/master work?
I don't think this patch would change anything, atleast it wouldn't get rid of the warning that Liu reported. Because, he is running his stress tests on a machine which has only 2 CPUs. So effectively, we are hotplugging only CPU1 (since CPU0 can't be taken offline, on Intel boxes).
Also, CPU1 is removed from cpu_active_mask during CPU_DOWN_PREPARE time itself, and migrate_tasks() comes much later (during CPU_DYING). And in any case, dest_cpu will never be CPU1, because it is the CPU that is going down. So it *has* to be CPU0 anyway.
So, I don't think changes to select_fallback_rq() to make it more careful is going to make any difference in the particular scenario that Liu is testing.
That said, even I don't know what the root cause of the warning is.. :-(
Regards, Srivatsa S. Bhat
>> > --- > include/linux/cpuset.h | 6 +--- > kernel/cpuset.c | 20 +++------------ > kernel/sched/core.c | 62 +++++++++++++++++++++++++++++++++++------------ > 3 files changed, 52 insertions(+), 36 deletions(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index e9eaec5..e0ffaf0 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -22,7 +22,7 @@ extern int cpuset_init(void); > extern void cpuset_init_smp(void); > extern void cpuset_update_active_cpus(void); > extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); > -extern int cpuset_cpus_allowed_fallback(struct task_struct *p); > +extern void 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); > @@ -144,10 +144,8 @@ 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) > +static inline void cpuset_cpus_allowed_fallback(struct task_struct *p) > { > - do_set_cpus_allowed(p, cpu_possible_mask); > - return cpumask_any(cpu_active_mask); > } > > static inline nodemask_t cpuset_mems_allowed(struct task_struct *p) > diff --git a/kernel/cpuset.c b/kernel/cpuset.c > index a09ac2b..c9837b7 100644 > --- a/kernel/cpuset.c > +++ b/kernel/cpuset.c > @@ -2195,7 +2195,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > mutex_unlock(&callback_mutex); > } > > -int cpuset_cpus_allowed_fallback(struct task_struct *tsk) > +void cpuset_cpus_allowed_fallback(struct task_struct *tsk) > { > const struct cpuset *cs; > int cpu; > @@ -2219,22 +2219,10 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk) > * 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. > + * > + * select_fallback_rq() will fix things ups and set cpu_possible_mask > + * if required. > */ > - > - 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. > - */ > - do_set_cpus_allowed(tsk, cpu_possible_mask); > - cpu = cpumask_any(cpu_active_mask); > - } > - > - return cpu; > } > > void cpuset_init_current_mems_allowed(void) > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index e37c9af..04d3f7f 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1263,29 +1263,59 @@ EXPORT_SYMBOL_GPL(kick_process); > */ > static int select_fallback_rq(int cpu, struct task_struct *p) > { > - int dest_cpu; > const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu)); > + enum { cpuset, possible, fail } state = cpuset; > + int dest_cpu; > > /* Look for allowed, online CPU in same node. */ > - for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask) > + for_each_cpu_mask(dest_cpu, *nodemask) { > + if (!cpu_online(dest_cpu)) > + continue; > + if (!cpu_active(dest_cpu)) > + continue; > if (cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p))) > return dest_cpu; > + } > > - /* Any allowed, online CPU? */ > - dest_cpu = cpumask_any_and(tsk_cpus_allowed(p), cpu_active_mask); > - if (dest_cpu < nr_cpu_ids) > - return dest_cpu; > + for (;;) { > + /* Any allowed, online CPU? */ > + for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) { > + if (!cpu_online(dest_cpu)) > + continue; > + if (!cpu_active(dest_cpu)) > + continue; > + goto out; > + } > > - /* No more Mr. Nice Guy. */ > - dest_cpu = cpuset_cpus_allowed_fallback(p); > - /* > - * Don't tell them about moving exiting tasks or > - * kernel threads (both mm NULL), since they never > - * leave kernel. > - */ > - if (p->mm && printk_ratelimit()) { > - printk_sched("process %d (%s) no longer affine to cpu%d\n", > - task_pid_nr(p), p->comm, cpu); > + switch (state) { > + case cpuset: > + /* No more Mr. Nice Guy. */ > + cpuset_cpus_allowed_fallback(p); > + state = possible; > + break; > + > + case possible: > + do_set_cpus_allowed(p, cpu_possible_mask); > + state = fail; > + break; > + > + case fail: > + BUG(); > + break; > + } > + } > + > +out: > + if (state != cpuset) { > + /* > + * Don't tell them about moving exiting tasks or > + * kernel threads (both mm NULL), since they never > + * leave kernel. > + */ > + if (p->mm && printk_ratelimit()) { > + printk_sched("process %d (%s) no longer affine to cpu%d\n", > + task_pid_nr(p), p->comm, cpu); > + } > } > > return dest_cpu; >
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