Re: [PATCHv2 1/1] RDMA/rxe: Fix a dead lock problem

[Yanjun Zhu <yanjun.zhu@linux.dev>]

在 2022/4/11 19:50, Jason Gunthorpe 写道:
> On Mon, Apr 11, 2022 at 04:00:18PM -0400, yanjun.zhu@linux.dev wrote:
>> @@ -138,8 +139,10 @@ 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,
>> -			      &pool->next, GFP_KERNEL);
>> +	xa_lock_irqsave(&pool->xa, flags);
>> +	err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
>> +				&pool->next, GFP_ATOMIC);
>> +	xa_unlock_irqrestore(&pool->xa, flags);
> 
> No to  using atomics, this needs to be either the _irq or _bh varient

If I understand you correctly, you mean that we should use 
xa_lock_irq/xa_unlock_irq or xa_lock_bh/xa_unlock_bh instead of 
xa_unlock_irqrestore?

If so, xa_lock_irq/xa_unlock_irq or xa_lock_bh/xa_unlock_bh is used 
here, the warning as below will appear. This means that 
__rxe_add_to_pool disables softirq, but fpu_clone enables softirq.

"
Apr 12 16:24:53 kernel: softirqs last  enabled at (13086): 
[<ffffffff91830d26>] fpu_clone+0xf6/0x570
Apr 12 16:24:53 kernel: softirqs last disabled at (13129): 
[<ffffffffc077f319>] __rxe_add_to_pool+0x49/0xa0 [rdma_rxe]
"

As such, it is better to use xa_unlock_irqrestore + 
__xa_alloc(...,GFP_ATOMIC/GFP_NOWAIT).

Zhu Yanjun

> 
> Jason