Re: [PATCH v6 mm-new 01/10] mm: thp: add support for BPF based THP order selection

[Yafang Shao <laoar.shao@gmail.com>]

On Wed, Aug 27, 2025 at 10:58 AM kernel test robot <lkp@intel.com> wrote:
>
> Hi Yafang,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on akpm-mm/mm-everything]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Yafang-Shao/mm-thp-add-support-for-BPF-based-THP-order-selection/20250826-152415
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/20250826071948.2618-2-laoar.shao%40gmail.com
> patch subject: [PATCH v6 mm-new 01/10] mm: thp: add support for BPF based THP order selection
> config: loongarch-randconfig-r113-20250827 (https://download.01.org/0day-ci/archive/20250827/202508271009.5neOZ0OG-lkp@intel.com/config)
> compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
> reproduce: (https://download.01.org/0day-ci/archive/20250827/202508271009.5neOZ0OG-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202508271009.5neOZ0OG-lkp@intel.com/

Thanks for the report .
It seems this sparse warning can be fixed with the below additional
change, would you please test it again?

diff --git a/mm/bpf_thp.c b/mm/bpf_thp.c
index 46b3bc96359e..b2f97f9e930d 100644
--- a/mm/bpf_thp.c
+++ b/mm/bpf_thp.c
@@ -5,27 +5,32 @@
 #include <linux/huge_mm.h>
 #include <linux/khugepaged.h>

+/**
+ * @get_suggested_order: Get the suggested THP orders for allocation
+ * @mm: mm_struct associated with the THP allocation
+ * @vma__nullable: vm_area_struct associated with the THP allocation
(may be NULL)
+ *                 When NULL, the decision should be based on @mm (i.e., when
+ *                 triggered from an mm-scope hook rather than a VMA-specific
+ *                 context).
+ *                 Must belong to @mm (guaranteed by the caller).
+ * @vma_flags: use these vm_flags instead of @vma->vm_flags (0 if @vma is NULL)
+ * @tva_flags: TVA flags for current @vma (-1 if @vma is NULL)
+ * @orders: Bitmask of requested THP orders for this allocation
+ *          - PMD-mapped allocation if PMD_ORDER is set
+ *          - mTHP allocation otherwise
+ *
+ * Rerurn: Bitmask of suggested THP orders for allocation. The highest
+ *         suggested order will not exceed the highest requested order
+ *         in @orders.
+ */
+typedef int suggested_order_fn_t(struct mm_struct *mm,
+                                struct vm_area_struct *vma__nullable,
+                                u64 vma_flags,
+                                enum tva_type tva_flags,
+                                int orders);
+
 struct bpf_thp_ops {
-       /**
-        * @get_suggested_order: Get the suggested THP orders for allocation
-        * @mm: mm_struct associated with the THP allocation
-        * @vma__nullable: vm_area_struct associated with the THP
allocation (may be NULL)
-        *                 When NULL, the decision should be based on
@mm (i.e., when
-        *                 triggered from an mm-scope hook rather than
a VMA-specific
-        *                 context).
-        *                 Must belong to @mm (guaranteed by the caller).
-        * @vma_flags: use these vm_flags instead of @vma->vm_flags (0
if @vma is NULL)
-        * @tva_flags: TVA flags for current @vma (-1 if @vma is NULL)
-        * @orders: Bitmask of requested THP orders for this allocation
-        *          - PMD-mapped allocation if PMD_ORDER is set
-        *          - mTHP allocation otherwise
-        *
-        * Rerurn: Bitmask of suggested THP orders for allocation. The highest
-        *         suggested order will not exceed the highest requested order
-        *         in @orders.
-        */
-       int (*get_suggested_order)(struct mm_struct *mm, struct
vm_area_struct *vma__nullable,
-                                  u64 vma_flags, enum tva_type
tva_flags, int orders) __rcu;
+       suggested_order_fn_t __rcu *get_suggested_order;
 };

 static struct bpf_thp_ops bpf_thp;
@@ -34,8 +39,7 @@ static DEFINE_SPINLOCK(thp_ops_lock);
 int get_suggested_order(struct mm_struct *mm, struct vm_area_struct
*vma__nullable,
                        u64 vma_flags, enum tva_type tva_flags, int orders)
 {
-       int (*bpf_suggested_order)(struct mm_struct *mm, struct
vm_area_struct *vma__nullable,
-                                  u64 vma_flags, enum tva_type
tva_flags, int orders);
+       suggested_order_fn_t *bpf_suggested_order;
        int suggested_orders = orders;

        /* No BPF program is attached */
@@ -106,10 +110,12 @@ static int bpf_thp_reg(void *kdata, struct bpf_link *link)

 static void bpf_thp_unreg(void *kdata, struct bpf_link *link)
 {
+       suggested_order_fn_t *old_fn;
+
        spin_lock(&thp_ops_lock);
        clear_bit(TRANSPARENT_HUGEPAGE_BPF_ATTACHED,
&transparent_hugepage_flags);
-       WARN_ON_ONCE(!rcu_access_pointer(bpf_thp.get_suggested_order));
-       rcu_replace_pointer(bpf_thp.get_suggested_order, NULL,
lockdep_is_held(&thp_ops_lock));
+       old_fn = rcu_replace_pointer(bpf_thp.get_suggested_order,
NULL, lockdep_is_held(&thp_ops_lock));
+       WARN_ON_ONCE(!old_fn);
        spin_unlock(&thp_ops_lock);

        synchronize_rcu();
@@ -117,8 +123,9 @@ static void bpf_thp_unreg(void *kdata, struct
bpf_link *link)

 static int bpf_thp_update(void *kdata, void *old_kdata, struct bpf_link *link)
 {
-       struct bpf_thp_ops *ops = kdata;
+       suggested_order_fn_t *old_fn, *new_fn;
        struct bpf_thp_ops *old = old_kdata;
+       struct bpf_thp_ops *ops = kdata;
        int ret = 0;

        if (!ops || !old)
@@ -130,9 +137,10 @@ static int bpf_thp_update(void *kdata, void
*old_kdata, struct bpf_link *link)
                ret = -ENOENT;
                goto out;
        }
-       WARN_ON_ONCE(!rcu_access_pointer(bpf_thp.get_suggested_order));
-       rcu_replace_pointer(bpf_thp.get_suggested_order,
ops->get_suggested_order,
-                           lockdep_is_held(&thp_ops_lock));
+
+       new_fn = rcu_dereference(ops->get_suggested_order);
+       old_fn = rcu_replace_pointer(bpf_thp.get_suggested_order,
new_fn, lockdep_is_held(&thp_ops_lock));
+       WARN_ON_ONCE(!old_fn || !new_fn);

 out:
        spin_unlock(&thp_ops_lock);
@@ -159,7 +167,7 @@ static int suggested_order(struct mm_struct *mm,
struct vm_area_struct *vma__nul
 }

 static struct bpf_thp_ops __bpf_thp_ops = {
-       .get_suggested_order = suggested_order,
+       .get_suggested_order = (suggested_order_fn_t __rcu *)suggested_order,
 };

 static struct bpf_struct_ops bpf_bpf_thp_ops = {


--
Regards

Yafang