On 05/11/2015 10:55 PM, Tejun Heo wrote:
> Hey,
>
> Prolly a better subject is "ensure attrs changes are properly
> synchronized"
>
> On Mon, May 11, 2015 at 05:35:50PM +0800, Lai Jiangshan wrote:
>> Current modification to attrs via sysfs is not atomically.
>
> atomic.
>
>>
>> Process A (change cpumask) | Process B (change numa affinity)
>> wq_cpumask_store() |
>> wq_sysfs_prep_attrs() |
> ^
> misaligned
It is aligned in email, misaligned in quoted email, and misaligned
in `git log` and `git show`, aligned in `git commit` when I wrote
the changelog.
I will just remove all the |.
>
>> | apply_workqueue_attrs()
>> apply_workqueue_attrs() |
>>
>> It results that the Process B's operation is totally reverted
>> without any notification.
>
> Yeah, right.
>
>> This behavior is acceptable but it is sometimes unexpected.
>
> I don't think this is an acceptable behavior.
>
>> Sequential model on non-performance-sensitive operations is more popular
>> and preferred. So this patch moves wq_sysfs_prep_attrs() into the protection
>
> You can just say the previous behavior is buggy.
It depends on definitions. To me, it is just a nuisance.
>
>> under wq_pool_mutex to ensure attrs-changing be sequentially.
>>
>> This patch is also a preparation patch for next patch which change
>> the API of apply_workqueue_attrs().
> ...
>> +static void apply_wqattrs_lock(void)
>> +{
>> + /*
>> + * CPUs should stay stable across pwq creations and installations.
>> + * Pin CPUs, determine the target cpumask for each node and create
>> + * pwqs accordingly.
>> + */
>> + get_online_cpus();
>> + mutex_lock(&wq_pool_mutex);
>> +}
>> +
>> +static void apply_wqattrs_unlock(void)
>> +{
>> + mutex_unlock(&wq_pool_mutex);
>> + put_online_cpus();
>> +}
>
> Separate out refactoring and extending locking coverage?
>
> Thanks.
>
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