Re: [PATCH bpf-next v3 1/3] bpf, arena: fix range_tree_clear inconsistency on kmalloc_nolock failure

[Emil Tsalapatis]

On Mon Aug 10, 2026 at 9:47 AM EDT, chenyuan_fl wrote:
> From: Yuan Chen <chenyuan@xxxxxxxxxx>
>
> range_tree_clear() pre-allocates the right-half node before modifying
> the tree, so an allocation failure returns -ENOMEM without altering the
> range tree.
>
> Signed-off-by: Yuan Chen <chenyuan@xxxxxxxxxx>

Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>

> ---
>  kernel/bpf/range_tree.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/bpf/range_tree.c b/kernel/bpf/range_tree.c
> index 2f28886f3ff7..15b588377a76 100644
> --- a/kernel/bpf/range_tree.c
> +++ b/kernel/bpf/range_tree.c
> @@ -143,16 +143,22 @@ int range_tree_clear(struct range_tree *rt, u32 start, u32 len)
>  		if (rn->rn_start < start && rn->rn_last > last) {
>  			u32 old_last = rn->rn_last;
>  
> +			/*
> +			 * Pre-allocate the right-half node before modifying
> +			 * the tree. If allocation fails we return -ENOMEM
> +			 * without altering the range tree.
> +			 */
> +			new_rn = kmalloc_nolock(sizeof(struct range_node),
> +						__GFP_ACCOUNT, NUMA_NO_NODE);
> +			if (!new_rn)
> +				return -ENOMEM;
> +
>  			/* Overlaps with the entire clearing range */
>  			range_it_remove(rn, rt);
>  			rn->rn_last = start - 1;
>  			range_it_insert(rn, rt);
>  
> -			/* Add a range */
> -			new_rn = kmalloc_nolock(sizeof(struct range_node), __GFP_ACCOUNT,
> -						NUMA_NO_NODE);
> -			if (!new_rn)
> -				return -ENOMEM;
> +			/* Add right-half range */
>  			new_rn->rn_start = last + 1;
>  			new_rn->rn_last = old_last;
>  			range_it_insert(new_rn, rt);