From: Yu Kuai <yukuai3@huawei.com>

ioprio works on the blk-cgroup level, all disks in the same cgroup
are the same, and the struct ioprio_blkg doesn't have anything in it.
Hence register the policy is enough, because cpd_alloc/free_fn will
be handled for each blk-cgroup, and there is no need to activate the
policy for disk.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-cgroup.c |  8 --------
 block/blk-ioprio.c | 45 ---------------------------------------------
 block/blk-ioprio.h |  9 ---------
 3 files changed, 62 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 37e6cc91d576..c7d00d95d499 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1458,7 +1458,6 @@ int blkcg_init_disk(struct gendisk *disk)
 	struct request_queue *q = disk->queue;
 	struct blkcg_gq *new_blkg, *blkg;
 	bool preloaded;
-	int ret;
 
 	new_blkg = blkg_alloc(&blkcg_root, disk, GFP_KERNEL);
 	if (!new_blkg)
@@ -1478,15 +1477,8 @@ int blkcg_init_disk(struct gendisk *disk)
 	if (preloaded)
 		radix_tree_preload_end();
 
-	ret = blk_ioprio_init(disk);
-	if (ret)
-		goto err_destroy_all;
-
 	return 0;
 
-err_destroy_all:
-	blkg_destroy_all(disk);
-	return ret;
 err_unlock:
 	spin_unlock_irq(&q->queue_lock);
 	if (preloaded)
diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
index ae52b418e984..8fff7ccc0ac7 100644
--- a/block/blk-ioprio.c
+++ b/block/blk-ioprio.c
@@ -49,14 +49,6 @@ static const char *policy_name[] = {
 
 static struct blkcg_policy ioprio_policy;
 
-/**
- * struct ioprio_blkg - Per (cgroup, request queue) data.
- * @pd: blkg_policy_data structure.
- */
-struct ioprio_blkg {
-	struct blkg_policy_data pd;
-};
-
 /**
  * struct ioprio_blkcg - Per cgroup data.
  * @cpd: blkcg_policy_data structure.
@@ -67,11 +59,6 @@ struct ioprio_blkcg {
 	enum prio_policy	 prio_policy;
 };
 
-static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
-{
-	return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
-}
-
 static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
 {
 	return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
@@ -108,25 +95,6 @@ static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
 	return nbytes;
 }
 
-static struct blkg_policy_data *
-ioprio_alloc_pd(struct gendisk *disk, struct blkcg *blkcg, gfp_t gfp)
-{
-	struct ioprio_blkg *ioprio_blkg;
-
-	ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
-	if (!ioprio_blkg)
-		return NULL;
-
-	return &ioprio_blkg->pd;
-}
-
-static void ioprio_free_pd(struct blkg_policy_data *pd)
-{
-	struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
-
-	kfree(ioprio_blkg);
-}
-
 static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
 {
 	struct ioprio_blkcg *blkcg;
@@ -169,9 +137,6 @@ static struct blkcg_policy ioprio_policy = {
 
 	.cpd_alloc_fn	= ioprio_alloc_cpd,
 	.cpd_free_fn	= ioprio_free_cpd,
-
-	.pd_alloc_fn	= ioprio_alloc_pd,
-	.pd_free_fn	= ioprio_free_pd,
 };
 
 void blkcg_set_ioprio(struct bio *bio)
@@ -209,16 +174,6 @@ void blkcg_set_ioprio(struct bio *bio)
 		bio->bi_ioprio = prio;
 }
 
-void blk_ioprio_exit(struct gendisk *disk)
-{
-	blkcg_deactivate_policy(disk, &ioprio_policy);
-}
-
-int blk_ioprio_init(struct gendisk *disk)
-{
-	return blkcg_activate_policy(disk, &ioprio_policy);
-}
-
 static int __init ioprio_init(void)
 {
 	return blkcg_policy_register(&ioprio_policy);
diff --git a/block/blk-ioprio.h b/block/blk-ioprio.h
index b6afb8e80de0..9265143f9bc9 100644
--- a/block/blk-ioprio.h
+++ b/block/blk-ioprio.h
@@ -9,17 +9,8 @@ struct request_queue;
 struct bio;
 
 #ifdef CONFIG_BLK_CGROUP_IOPRIO
-int blk_ioprio_init(struct gendisk *disk);
-void blk_ioprio_exit(struct gendisk *disk);
 void blkcg_set_ioprio(struct bio *bio);
 #else
-static inline int blk_ioprio_init(struct gendisk *disk)
-{
-	return 0;
-}
-static inline void blk_ioprio_exit(struct gendisk *disk)
-{
-}
 static inline void blkcg_set_ioprio(struct bio *bio)
 {
 }
-- 
2.39.2

On 7/11/24 2:00 AM, Yu Kuai wrote:
> ioprio works on the blk-cgroup level, all disks in the same cgroup
> are the same, and the struct ioprio_blkg doesn't have anything in it.
> Hence register the policy is enough, because cpd_alloc/free_fn will
> be handled for each blk-cgroup, and there is no need to activate the
> policy for disk.

As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
pointers are NULL. Hence my question why this patch does not trigger any
NULL pointer dereferences?

Thanks,

Bart.

Hi,

在 2024/07/12 2:03, Bart Van Assche 写道:
> On 7/11/24 2:00 AM, Yu Kuai wrote:
>> ioprio works on the blk-cgroup level, all disks in the same cgroup
>> are the same, and the struct ioprio_blkg doesn't have anything in it.
>> Hence register the policy is enough, because cpd_alloc/free_fn will
>> be handled for each blk-cgroup, and there is no need to activate the
>> policy for disk.
> 
> As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
> none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
> pointers are NULL. Hence my question why this patch does not trigger any
> NULL pointer dereferences?

Because the blkcg_deactivate_policy() is removed as well, there are no
callers now... blkcg_policy_register() is still called to make sure
cpd_(alloc|free)_fn will still be called.

Thanks,
Kuai

> 
> Thanks,
> 
> Bart.
> .
> 

On Fri, Jul 12, 2024 at 09:10:30AM +0800, Yu Kuai wrote:
> > As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
> > none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
> > pointers are NULL. Hence my question why this patch does not trigger any
> > NULL pointer dereferences?
> 
> Because the blkcg_deactivate_policy() is removed as well, there are no
> callers now... blkcg_policy_register() is still called to make sure
> cpd_(alloc|free)_fn will still be called.

Can you throw in a patch documenting this?  Any maybe add a check
that pd_alloc_fn / pd_free_fn exist in blkcg_activate_policy and
WARN and return an error otherwise?

Hi,

在 2024/07/12 13:22, Christoph Hellwig 写道:
> On Fri, Jul 12, 2024 at 09:10:30AM +0800, Yu Kuai wrote:
>>> As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
>>> none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
>>> pointers are NULL. Hence my question why this patch does not trigger any
>>> NULL pointer dereferences?
>>
>> Because the blkcg_deactivate_policy() is removed as well, there are no
>> callers now... blkcg_policy_register() is still called to make sure
>> cpd_(alloc|free)_fn will still be called.
> 
> Can you throw in a patch documenting this?  Any maybe add a check
> that pd_alloc_fn / pd_free_fn exist in blkcg_activate_policy and
> WARN and return an error otherwise?

Of course, I realized now that just mention don't activate the policy
from commit message is too little explanation.

Thanks,
Kuai

> 
> .
> 

Hi,

在 2024/07/12 9:10, Yu Kuai 写道:
> Hi,
> 
> 在 2024/07/12 2:03, Bart Van Assche 写道:
>> On 7/11/24 2:00 AM, Yu Kuai wrote:
>>> ioprio works on the blk-cgroup level, all disks in the same cgroup
>>> are the same, and the struct ioprio_blkg doesn't have anything in it.
>>> Hence register the policy is enough, because cpd_alloc/free_fn will
>>> be handled for each blk-cgroup, and there is no need to activate the
>>> policy for disk.
>>
>> As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
>> none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
>> pointers are NULL. Hence my question why this patch does not trigger any
>> NULL pointer dereferences?
> 
> Because the blkcg_deactivate_policy() is removed as well, there are no

Sorry about the typo, blkcg_activate_policy() is removed, all the places
of pd_(alloc|free)_fn can't be reached.

Thanks,
Kuai

> callers now... blkcg_policy_register() is still called to make sure
> cpd_(alloc|free)_fn will still be called.
> 
> Thanks,
> Kuai
> 
>>
>> Thanks,
>>
>> Bart.
>> .
>>
> 
> .
>