Re: [PATCH] bpf: Use refcount_t instead of atomic_t for mmap_count

Pei Xiao
2024-12-31T03:00:34Z

在 2024/12/31 00:40, Jiri Olsa 写道:
> On Mon, Dec 30, 2024 at 03:16:55PM +0800, Pei Xiao wrote:
>> Use an API that resembles more the actual use of mmap_count.
>
> I'm not sure I understand the issue, could you provide more details?
>
hi,
refcount_t type which allows us to catch overflow and underflow issues.

thanks!
Pei.
> thanks,
> jirka
>
>>
>> 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@intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202412292037.LXlYSHKl-lkp@intel.com/
>> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
>> ---
>> kernel/bpf/arena.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
>> index 945a5680f6a5..8caf56a308d9 100644
>> --- a/kernel/bpf/arena.c
>> +++ b/kernel/bpf/arena.c
>> @@ -218,7 +218,7 @@ 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)
>> @@ -228,7 +228,7 @@ 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);
>> @@ -239,7 +239,7 @@ 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)
>> @@ -248,7 +248,7 @@ 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 */
>> --
>> 2.25.1
>>
>>