netdev - Re: [PATCH 1/1] s390/ism: fix concurrency management in ism

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Message-ID: <af7298f5-08a0-4492-834d-a348144c909e@linux.ibm.com>
Date: Mon, 21 Jul 2025 10:17:30 +0200
From: Alexandra Winter <wintera@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller"
 <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Thorsten Winkler <twinkler@...ux.ibm.com>,
        Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Sebastian Ott <sebott@...ux.ibm.com>,
        Ursula Braun <ubraun@...ux.ibm.com>, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Aliaksei Makarau <Aliaksei.Makarau@....com>,
        Mahanta Jambigi <mjambigi@...ux.ibm.com>
Subject: Re: [PATCH 1/1] s390/ism: fix concurrency management in ism_cmd()



On 21.07.25 09:30, Alexander Gordeev wrote:
> On Sun, Jul 20, 2025 at 11:11:09PM +0200, Halil Pasic wrote:
> 
> Hi Halil,
> 
> ...
>> @@ -129,7 +129,9 @@ static int ism_cmd(struct ism_dev *ism, void *cmd)
>>  {
>>  	struct ism_req_hdr *req = cmd;
>>  	struct ism_resp_hdr *resp = cmd;
>> +	unsigned long flags;
>>  
>> +	spin_lock_irqsave(&ism->cmd_lock, flags);
> 
> I only found smcd_handle_irq() scheduling a tasklet, but no commands issued.
> Do we really need disable interrupts?

You are right in current code, the interrupt and event handlers of ism and smcd
never issue a control command that calls ism_cmd().
OTOH, future ism clients could do that.
The control commands are not part of the data path, but of connection establish.
So I don't really expect a performance impact.
I have it on my ToDo list, to change this to threaded interrupts in the future.
So no strong opinion on my side.
Simple spin_lock is fine with me.



> 
>>  	__ism_write_cmd(ism, req + 1, sizeof(*req), req->len - sizeof(*req));
>>  	__ism_write_cmd(ism, req, 0, sizeof(*req));
>>  
>> @@ -143,6 +145,7 @@ static int ism_cmd(struct ism_dev *ism, void *cmd)
>>  	}
>>  	__ism_read_cmd(ism, resp + 1, sizeof(*resp), resp->len - sizeof(*resp));
>>  out:
>> +	spin_unlock_irqrestore(&ism->cmd_lock, flags);
>>  	return resp->ret;
>>  }
>>  
> ...
> 
> Thanks!
>