On 02/06/2013 07:55 PM, Andrew Morton wrote:
> On Wed, 30 Jan 2013 21:00:22 -0500
> Sasha Levin <sasha.le...@oracle.com> wrote:
>
>> I'm not sure why, but the hlist for each entry iterators were conceived
>> differently from the list ones. While the list ones are nice and elegant:
>>
>> list_for_each_entry(pos, head, member)
>>
>> The hlist ones were greedy and wanted an extra parameter:
>>
>> hlist_for_each_entry(tpos, pos, head, member)
>>
>> Why did they need an extra pos parameter? I'm not quite sure. Not only
>> they don't really need it, it also prevents the iterator from looking
>> exactly like the list iterator, which is unfortunate.
>>
>> Besides the semantic patch, there was some manual work required:
>>
>> - Fix up the actual hlist iterators in linux/list.h
>> - Fix up the declaration of other iterators based on the hlist ones.
>> - A very small amount of places were using the 'node' parameter, this
>> was modified to use 'obj->member' instead.
>> - Coccinelle didn't handle the hlist_for_each_entry_safe iterator
>> properly, so those had to be fixed up manually.
>>
>> ...
>>
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>>
>> ...
>>
>> @@ -4525,7 +4524,7 @@ int __init_or_module cgroup_load_subsys(struct
>> cgroup_subsys *ss)
>> * this is all done under the css_set_lock.
>> */
>> write_lock(&css_set_lock);
>> - hash_for_each_safe(css_set_table, i, node, tmp, cg, hlist) {
>> + hash_for_each_safe(css_set_table, i, tmp, cg, hlist) {
>> /* skip entries that we already rehashed */
>> if (cg->subsys[ss->subsys_id])
>> continue;
>
> Problems in cgroup_load_subsys().
>
> In linux-next, that function is now using the `node' storage which your
> patch removes:
>
> @@ -4503,23 +4525,17 @@ int __init_or_module cgroup_load_subsys(struct
> cgroup_subsys *ss)
> * this is all done under the css_set_lock.
> */
> write_lock(&css_set_lock);
> - for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
> - struct css_set *cg;
> - struct hlist_node *node, *tmp;
> - struct hlist_head *bucket = &css_set_table[i], *new_bucket;
> -
> - hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
> - /* skip entries that we already rehashed */
> - if (cg->subsys[ss->subsys_id])
> - continue;
> - /* remove existing entry */
> - hlist_del(&cg->hlist);
> - /* set new value */
> - cg->subsys[ss->subsys_id] = css;
> - /* recompute hash and restore entry */
> - new_bucket = css_set_hash(cg->subsys);
> - hlist_add_head(&cg->hlist, new_bucket);
> - }
> + hash_for_each_safe(css_set_table, i, node, tmp, cg, hlist) {
> + /* skip entries that we already rehashed */
> + if (cg->subsys[ss->subsys_id])
> + continue;
> + /* remove existing entry */
> + hash_del(&cg->hlist);
> + /* set new value */
> + cg->subsys[ss->subsys_id] = css;
> + /* recompute hash and restore entry */
> + key = css_set_hash(cg->subsys);
> + hash_add(css_set_table, node, key); <<<<---- here
> }
> write_unlock(&css_set_lock);
>
>
>
> This didn't show up (apart from a "used unintialized" warning) because
> your patch forgot to remove the definition of `node'.
Yikes, sorry :(
Coccinelle can't properly handle the case of removing just one
variable out of a declaration of two in the same line, and it has
slipped through my manual pass afterwards.
fwiw, I've solved all similar cases in the same way: "node" became
"obj->member".
Thanks,
Sasha
> I did this. Tejun, could you please opine?
>
>
> @@ -4456,7 +4455,7 @@ int __init_or_module cgroup_load_subsys(
> {
> struct cgroup_subsys_state *css;
> int i, ret;
> - struct hlist_node *node, *tmp;
> + struct hlist_node *tmp;
> struct css_set *cg;
> unsigned long key;
>
> @@ -4534,7 +4533,7 @@ int __init_or_module cgroup_load_subsys(
> cg->subsys[ss->subsys_id] = css;
> /* recompute hash and restore entry */
> key = css_set_hash(cg->subsys);
> - hash_add(css_set_table, node, key);
> + hash_add(css_set_table, &cg->hlist, key);
> }
> write_unlock(&css_set_lock);
>
>
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