On Thu, Nov 14, 2024 at 7:53 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
> When running bpf selftest (./test_progs -j), the following warnings
> showed up:
>
> $ ./test_progs -t arena_atomics
> ...
> BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u19:0/12501
> caller is bpf_mem_free+0x128/0x330
> ...
> Call Trace:
> <TASK>
> dump_stack_lvl
> check_preemption_disabled
> bpf_mem_free
> range_tree_destroy
> arena_map_free
> bpf_map_free_deferred
> process_scheduled_works
> ...
>
> For selftests arena_htab and arena_list, similar smp_process_id() BUGs are
> dumped, and the following are two stack trace:
>
> <TASK>
> dump_stack_lvl
> check_preemption_disabled
> bpf_mem_alloc
> range_tree_set
> arena_map_alloc
> map_create
> ...
>
> <TASK>
> dump_stack_lvl
> check_preemption_disabled
> bpf_mem_alloc
> range_tree_clear
> arena_vm_fault
> do_pte_missing
> handle_mm_fault
> do_user_addr_fault
> ...
>
> Adding migrate_{disable,enable}() around related arena_*() calls can fix the issue.
>
> Fixes: b795379757eb ("bpf: Introduce range_tree data structure and use it in bpf arena")
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> kernel/bpf/arena.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> index 3e1dfe349ced..9a55d18032a4 100644
> --- a/kernel/bpf/arena.c
> +++ b/kernel/bpf/arena.c
> @@ -134,7 +134,9 @@ static struct bpf_map *arena_map_alloc(union bpf_attr *attr)
> INIT_LIST_HEAD(&arena->vma_list);
> bpf_map_init_from_attr(&arena->map, attr);
> range_tree_init(&arena->rt);
> + migrate_disable();
> range_tree_set(&arena->rt, 0, attr->max_entries);
> + migrate_enable();
> mutex_init(&arena->lock);
>
> return &arena->map;
> @@ -185,7 +187,9 @@ static void arena_map_free(struct bpf_map *map)
> apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena),
> KERN_VM_SZ - GUARD_SZ, existing_page_cb, NULL);
> free_vm_area(arena->kern_vm);
> + migrate_disable();
> range_tree_destroy(&arena->rt);
> + migrate_enable();
> bpf_map_area_free(arena);
> }
>
> @@ -276,7 +280,9 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
> /* User space requested to segfault when page is not allocated by bpf prog */
> return VM_FAULT_SIGSEGV;
>
> + migrate_disable();
> ret = range_tree_clear(&arena->rt, vmf->pgoff, 1);
> + migrate_enable();
Thanks for the fix.
I thought I had all debug configs enabled :(
Could you please add migrate_disable/enable into range_tree.c
around bpf_mem_alloc/free calls instead ?
range_tree user shouldn't need to worry about this internal details.
pw-bot: cr
