On Fri, Oct 3, 2025 at 1:47 AM KaFai Wan <[email protected]> wrote:
>
> When unpinning a BPF hash table (htab or htab_lru) that contains internal
> structures (timer, workqueue, or task_work) in its values, a BUG warning
> is triggered:
> BUG: sleeping function called from invalid context at
> kernel/bpf/hashtab.c:244
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 14, name: ksoftirqd/0
> ...
>
> The issue arises from the interaction between BPF object unpinning and
> RCU callback mechanisms:
> 1. BPF object unpinning uses ->free_inode() which schedules cleanup via
> call_rcu(), deferring the actual freeing to an RCU callback that
> executes within the RCU_SOFTIRQ context.
> 2. During cleanup of hash tables containing internal structures,
> htab_map_free_internal_structs() is invoked, which includes
> cond_resched() or cond_resched_rcu() calls to yield the CPU during
> potentially long operations.
>
> However, cond_resched() or cond_resched_rcu() cannot be safely called from
> atomic RCU softirq context, leading to the BUG warning when attempting
> to reschedule.
>
> Fix this by changing from ->free_inode() to ->destroy_inode() for BPF
> objects (prog, map, link). This allows direct inode freeing without
> RCU callback scheduling, avoiding the invalid context warning.
>
> Reported-by: Le Chen <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Fixes: 68134668c17f ("bpf: Add map side support for bpf timers.")
> Suggested-by: Alexei Starovoitov <[email protected]>
> Signed-off-by: KaFai Wan <[email protected]>
> ---
> kernel/bpf/inode.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
> index f90bdcc0a047..65c2a71d7de1 100644
> --- a/kernel/bpf/inode.c
> +++ b/kernel/bpf/inode.c
> @@ -790,7 +790,7 @@ const struct super_operations bpf_super_ops = {
> .statfs = simple_statfs,
> .drop_inode = inode_just_drop,
> .show_options = bpf_show_options,
> - .free_inode = bpf_free_inode,
> + .destroy_inode = bpf_free_inode,
s/bpf_free_inode/bpf_destroy_inode/ then?
> };
>
> enum {
> --
> 2.43.0
>
