blk-cgroup: improve policy registration error handling

This patch improve the returned error code of blkcg_policy_register().

1. Move the validation check for cpd/pd_alloc_fn and cpd/pd_free_fn
   function pairs to the start of blkcg_policy_register(). This ensures
   we immediately return -EINVAL if the function pairs are not correctly
   provided, rather than returning -ENOSPC after locking and unlocking
   mutexes unnecessarily.

   Those locks should not contention any problems, as error of policy
   registration is a super cold path.

2. Return -ENOMEM when cpd_alloc_fn() failed.

Co-authored-by: Wen Tao <wentao@uniontech.com>
Signed-off-by: Wen Tao <wentao@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/3E333A73B6B6DFC0+20250317022924.150907-1-chenlinxuan@uniontech.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 9ed93d91d754ab47a22fc7d55506f6acc34fc6a2..2609f7294427a3574eb3b36d40f13ea8bb74ac4f 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1727,27 +1727,27 @@ int blkcg_policy_register(struct blkcg_policy *pol)
        struct blkcg *blkcg;
        int i, ret;
 
+       /*
+        * Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs, and policy
+        * without pd_alloc_fn/pd_free_fn can't be activated.
+        */
+       if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
+           (!pol->pd_alloc_fn ^ !pol->pd_free_fn))
+               return -EINVAL;
+
        mutex_lock(&blkcg_pol_register_mutex);
        mutex_lock(&blkcg_pol_mutex);
 
        /* find an empty slot */
-       ret = -ENOSPC;
        for (i = 0; i < BLKCG_MAX_POLS; i++)
                if (!blkcg_policy[i])
                        break;
        if (i >= BLKCG_MAX_POLS) {
                pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
+               ret = -ENOSPC;
                goto err_unlock;
        }
 
-       /*
-        * Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs, and policy
-        * without pd_alloc_fn/pd_free_fn can't be activated.
-        */
-       if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
-           (!pol->pd_alloc_fn ^ !pol->pd_free_fn))
-               goto err_unlock;
-
        /* register @pol */
        pol->plid = i;
        blkcg_policy[pol->plid] = pol;
@@ -1758,8 +1758,10 @@ int blkcg_policy_register(struct blkcg_policy *pol)
                        struct blkcg_policy_data *cpd;
 
                        cpd = pol->cpd_alloc_fn(GFP_KERNEL);
-                       if (!cpd)
+                       if (!cpd) {
+                               ret = -ENOMEM;
                                goto err_free_cpds;
+                       }
 
                        blkcg->cpd[pol->plid] = cpd;
                        cpd->blkcg = blkcg;