Patch "bpf: Use refcount_t instead of atomic_t for mmap_count" has been added to the 6.12-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Use refcount_t instead of atomic_t for mmap_count

to the 6.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-use-refcount_t-instead-of-atomic_t-for-mmap_coun.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b41e0c1001a9a35de98b52bcf19d023689460fe0
Author: Pei Xiao <xiaopei01@xxxxxxxxxx>
Date:   Mon Dec 30 15:16:55 2024 +0800

    bpf: Use refcount_t instead of atomic_t for mmap_count
    
    [ Upstream commit dfa94ce54f4139c893b9c4ec17df6f7c6a7515d3 ]
    
    Use an API that resembles more the actual use of mmap_count.
    
    Found by cocci:
    kernel/bpf/arena.c:245:6-25: WARNING: atomic_dec_and_test variation before object free at line 249.
    
    Fixes: b90d77e5fd78 ("bpf: Fix remap of arena.")
    Reported-by: kernel test robot <lkp@xxxxxxxxx>
    Closes: https://lore.kernel.org/oe-kbuild-all/202412292037.LXlYSHKl-lkp@xxxxxxxxx/
    Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/6ecce439a6bc81adb85d5080908ea8959b792a50.1735542814.git.xiaopei01@xxxxxxxxxx
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index e52b3ad231b9c..93e48c7cad4ef 100644
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -212,7 +212,7 @@ static u64 arena_map_mem_usage(const struct bpf_map *map)
 struct vma_list {
 	struct vm_area_struct *vma;
 	struct list_head head;
-	atomic_t mmap_count;
+	refcount_t mmap_count;
 };
 
 static int remember_vma(struct bpf_arena *arena, struct vm_area_struct *vma)
@@ -222,7 +222,7 @@ static int remember_vma(struct bpf_arena *arena, struct vm_area_struct *vma)
 	vml = kmalloc(sizeof(*vml), GFP_KERNEL);
 	if (!vml)
 		return -ENOMEM;
-	atomic_set(&vml->mmap_count, 1);
+	refcount_set(&vml->mmap_count, 1);
 	vma->vm_private_data = vml;
 	vml->vma = vma;
 	list_add(&vml->head, &arena->vma_list);
@@ -233,7 +233,7 @@ static void arena_vm_open(struct vm_area_struct *vma)
 {
 	struct vma_list *vml = vma->vm_private_data;
 
-	atomic_inc(&vml->mmap_count);
+	refcount_inc(&vml->mmap_count);
 }
 
 static void arena_vm_close(struct vm_area_struct *vma)
@@ -242,7 +242,7 @@ static void arena_vm_close(struct vm_area_struct *vma)
 	struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
 	struct vma_list *vml = vma->vm_private_data;
 
-	if (!atomic_dec_and_test(&vml->mmap_count))
+	if (!refcount_dec_and_test(&vml->mmap_count))
 		return;
 	guard(mutex)(&arena->lock);
 	/* update link list under lock */