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

[Bob Pearson <rpearsonhpe@gmail.com>]

On 4/10/22 22:06, Bart Van Assche wrote:
> 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.

You're right. I missed that. Zhu wants to write the patch so hopefully he's on top of that.
For now we could use GFP_ATOMIC.

Bob