Re: [PATCH] mm/vmalloc: Do not trigger BUG() on BH disabled context

[Baoquan He]

On 05/15/26 at 05:30pm, Uladzislau Rezki (Sony) wrote:
> __get_vm_area_node() currently triggers a BUG() if in_interrupt()
> returns true. However, in_interrupt() also reports true when BH
> are disabled.
> 
> The bridge code can call rhashtable_lookup_insert_fast() with
> bottom halves disabled:
> 
> __vlan_add()
>  -> br_fdb_add_local()
>   spin_lock_bh(&br->hash_lock); <-- Disable BH
>    -> fdb_add_local()
>     -> fdb_create()
>      -> rhashtable_lookup_insert_fast()
>       -> kvmalloc()
>        -> vmalloc()
>         -> __get_vm_area_node()
>          -> BUG_ON(in_interrupt())
>   spin_unlock_bh(&br->hash_lock)
> 
> this triggers the BUG() despite the caller not being in NMI or
> hard IRQ context.

Because the current vmalloc supports non-blocking allocation, so we
need to skip disabled BH or in_serving_softirq() cases to avoid unwanted
BUG(). This change looks great to me, not sure if I undersand it
correctly.

Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>

Thanks
Baoquan

> 
> Replace the in_interrupt() check with in_nmi() || in_hardirq().
> 
> Cc: Ido Schimmel <idosch@xxxxxxxxxx>
> Fixes: c6307674ed82 ("mm: kvmalloc: add non-blocking support for vmalloc")
> Reported-by: syzbot+8b12fc6e0fb139765b58@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/all/69ff8c7c.050a0220.1036b8.000b.GAE@xxxxxxxxxx/
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 676851d5cfe7..273bbe49eaef 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3209,7 +3209,7 @@ struct vm_struct *__get_vm_area_node(unsigned long size,
>  	struct vm_struct *area;
>  	unsigned long requested_size = size;
>  
> -	BUG_ON(in_interrupt());
> +	BUG_ON(in_nmi() || in_hardirq());
>  	size = ALIGN(size, 1ul << shift);
>  	if (unlikely(!size))
>  		return NULL;
> -- 
> 2.47.3
>