Re: [PATCH for-next] RDMA/rxe: Fix "Replace red-black trees by xarrays"

[Bart Van Assche <bvanassche@acm.org>]

On 4/10/22 15:39, Bob Pearson wrote:
> Fixes: 3225717f6dfa ("RDMA/rxe: Replace red-black trees by carrays")
                                                              ^^^^^^^
                                                              xarrays?

> @@ -138,8 +140,10 @@ void *rxe_alloc(struct rxe_pool *pool)
>   	elem->obj = obj;
>   	kref_init(&elem->ref_cnt);
>   
> -	err = xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> +	xa_lock_irqsave(xa, flags);
> +	err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
>   			      &pool->next, GFP_KERNEL);
> +	xa_unlock_irqrestore(xa, flags);

Please take a look at the xas_unlock_type() and xas_lock_type() calls in 
__xas_nomem(). I think that the above change will trigger a GFP_KERNEL 
allocation with interrupts disabled. My understanding is that GFP_KERNEL 
allocations may sleep and hence that the above code may cause 
__xas_nomem() to sleep with interrupts disabled. I don't think that is 
allowed.

Thanks,

Bart.