linux-kernel - Re: [PATCH net] net/smc: Transfer remaining wait queue entries during fallback

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Date:   Fri, 12 Nov 2021 23:28:11 +0800
From:   Wen Gu <guwen@...ux.alibaba.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     kgraul@...ux.ibm.com, davem@...emloft.net, kuba@...nel.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, tonylu@...ux.alibaba.com,
        dust.li@...ux.alibaba.com, xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH net] net/smc: Transfer remaining wait queue entries during
 fallback



On 2021/11/12 10:02 pm, Heiko Carstens wrote:
> On Fri, Nov 12, 2021 at 11:30:39AM +0800, Wen Gu wrote:
> ...
>> +	wait_queue_head_t *smc_wait = sk_sleep(&smc->sk);
>> +	wait_queue_head_t *clc_wait = sk_sleep(smc->clcsock->sk);
>> +	unsigned long flags;
>> +
>>   	smc->use_fallback = true;
>>   	smc->fallback_rsn = reason_code;
>>   	smc_stat_fallback(smc);
>> @@ -571,6 +575,16 @@ static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
>>   		smc->clcsock->file->private_data = smc->clcsock;
>>   		smc->clcsock->wq.fasync_list =
>>   			smc->sk.sk_socket->wq.fasync_list;
>> +
>> +		/* There might be some wait queue entries remaining
>> +		 * in smc socket->wq, which should be removed to
>> +		 * clcsocket->wq during the fallback.
>> +		 */
>> +		spin_lock_irqsave(&smc_wait->lock, flags);
>> +		spin_lock_irqsave(&clc_wait->lock, flags);
>> +		list_splice_init(&smc_wait->head, &clc_wait->head);
>> +		spin_unlock_irqrestore(&clc_wait->lock, flags);
>> +		spin_unlock_irqrestore(&smc_wait->lock, flags);
> 
> No idea if the rest of the patch makes sense, however this usage of
> spin_lock_irqsave() is not correct. The second spin_lock_irqsave()
> would always save a state with irqs disabled into "flags", and
> therefore this path would always be left with irqs disabled,
> regardless if irqs were enabled or disabled when entering.
> 
> You need to change it to something like
> 
>> +		spin_lock_irqsave(&smc_wait->lock, flags);
>> +		spin_lock(&clc_wait->lock);
>> +		list_splice_init(&smc_wait->head, &clc_wait->head);
>> +		spin_unlock(&clc_wait->lock);
>> +		spin_unlock_irqrestore(&smc_wait->lock, flags);

Sorry for the mistake... I will correct this.

Thanks,
Wen Gu