Joshua Hahn <joshua.hahnjy@xxxxxxxxx> writes:
> On Wed, 12 Feb 2025 10:49:32 +0800 "Huang, Ying" <ying.huang@xxxxxxxxxxxxxxxxx> wrote:
>
>> Hi, Joshua,
>>
>> Thanks for your patch and sorry for late reply.
>
> Hi Ying, no worries! Thank you for taking time to review this patch.
>
>> Joshua Hahn <joshua.hahnjy@xxxxxxxxx> writes:
[snip]
>> > +
>> > +static ssize_t weighted_interleave_mode_store(struct kobject *kobj,
>> > + struct kobj_attribute *attr, const char *buf, size_t count)
>> > +{
>> > + uint64_t *bw;
>> > + u8 *old_iw, *new_iw;
>> > +
>> > + if (count == 0)
>> > + return -EINVAL;
>> > +
>> > + if (sysfs_streq(buf, "N") || sysfs_streq(buf, "0")) {
>>
>> kstrtobool() can be used here. It can deal with 'count == 0' case too.
>
> These kernel string tools are very helpful, thank you for bringing
> them to my attention : -)
>
>> > + weighted_interleave_auto = false;
>> > + return count;
>> > + } else if (!sysfs_streq(buf, "Y") && !sysfs_streq(buf, "1")) {
>> > + return -EINVAL;
>> > + }
>> > +
>> > + new_iw = kcalloc(nr_node_ids, sizeof(u8), GFP_KERNEL);
>> > + if (!new_iw)
>> > + return -ENOMEM;
>> > +
>> > + mutex_lock(&iw_table_lock);
>> > + bw = node_bw_table;
>> > +
>> > + if (!bw) {
>> > + mutex_unlock(&iw_table_lock);
>> > + kfree(new_iw);
>> > + return -ENODEV;
>> > + }
>> > +
>> > + old_iw = rcu_dereference_protected(iw_table,
>> > + lockdep_is_held(&iw_table_lock));
>> > +
>> > + reduce_interleave_weights(bw, new_iw);
>> > + rcu_assign_pointer(iw_table, new_iw);
>> > + mutex_unlock(&iw_table_lock);
>> > +
>> > + synchronize_rcu();
>> > + kfree(old_iw);
>> > +
>> > + weighted_interleave_auto = true;
>>
>> Why assign weighted_interleave_auto after synchronize_rcu()? To reduce
>> the race window, it's better to change weighted_interleave_auto and
>> iw_table together? Is it better to put them into a data structure and
>> change them together always?
>>
>> struct weighted_interleave_state {
>> bool weighted_interleave_auto;
>> u8 iw_table[0]
>> };
>
> I see, I think your explanation makes sense. For the first question,
> I think your point makes sense, so I will move the updating to be
> inside the rcu section.
>
> As for the combined data structure, I think that this makes sense,
> but I have a few thoughts. First, there are some times when we don't
> update both of them, like moving from auto --> manual, and whenever
> we just update iw_table, we don't need to update the weighted_interleave
> auto field. I also have a concern that this might make the code a bit
> harder to read, but that is just my humble opinion.
I think the overhead is relatively small. With that, we can avoid the
inconsistency between weighted_interleave_auto and iw_table[].
struct_size() or struct_size_t() family helpers can be used to manage
the flexible array at the end of the struct.
---
Best Regards,
Huang, Ying
