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SubjectRe: [PATCH 3/6] cpuset: convert cpuset_attach() to use cpumask_var_t
Andrew Morton wrote:
> On Mon, 05 Jan 2009 16:47:21 +0800 Li Zefan <lizf@cn.fujitsu.com> wrote:
>
>> Allocate a global cpumask_var_t at boot, and use it in cpuset_attach(), so
>> we won't fail cpuset_attach().
>>
>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
>> Acked-by: Mike Travis <travis@sgi.com>
>> ---
>> kernel/cpuset.c | 14 +++++++++-----
>> 1 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
>> index afa29cf..1e32e6b 100644
>> --- a/kernel/cpuset.c
>> +++ b/kernel/cpuset.c
>> @@ -1306,6 +1306,9 @@ static int fmeter_getrate(struct fmeter *fmp)
>> return val;
>> }
>>
>> +/* Protected by cgroup_lock */
>> +static cpumask_var_t cpus_attach;
>> +
>> /* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
>> static int cpuset_can_attach(struct cgroup_subsys *ss,
>> struct cgroup *cont, struct task_struct *tsk)
>> @@ -1330,7 +1333,6 @@ static void cpuset_attach(struct cgroup_subsys *ss,
>> struct cgroup *cont, struct cgroup *oldcont,
>> struct task_struct *tsk)
>> {
>> - cpumask_t cpus;
>> nodemask_t from, to;
>> struct mm_struct *mm;
>> struct cpuset *cs = cgroup_cs(cont);
>> @@ -1338,13 +1340,13 @@ static void cpuset_attach(struct cgroup_subsys *ss,
>> int err;
>>
>> if (cs == &top_cpuset) {
>> - cpus = cpu_possible_map;
>> + cpumask_copy(cpus_attach, cpu_possible_mask);
>> } else {
>> mutex_lock(&callback_mutex);
>> - guarantee_online_cpus(cs, &cpus);
>> + guarantee_online_cpus(cs, cpus_attach);
>> mutex_unlock(&callback_mutex);
>> }
>> - err = set_cpus_allowed_ptr(tsk, &cpus);
>> + err = set_cpus_allowed_ptr(tsk, cpus_attach);
>> if (err)
>> return;
>>
>> @@ -1357,7 +1359,6 @@ static void cpuset_attach(struct cgroup_subsys *ss,
>> cpuset_migrate_mm(mm, &from, &to);
>> mmput(mm);
>> }
>> -
>> }
>>
>> /* The various types of files and directories in a cpuset file system */
>> @@ -1838,6 +1839,9 @@ int __init cpuset_init(void)
>> if (err < 0)
>> return err;
>>
>> + if (!alloc_cpumask_var(&cpus_attach, GFP_KERNEL))
>> + BUG();
>> +
>> number_of_cpusets = 1;
>> return 0;
>> }
>
> OK, that works.
>
> Do we need to dynamically allocate cpus_attach? Can we just do
>
> static cpumask_t cpus_attach;
>
> ?
>

Yes, it's used by cpuset_attach() only, and cpuset_attach() is called with
cgroup_lock() held, so it won't happen that 2 threads access cpus_attach
concurrently.



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