netdev - RE: [PATCH] iavf: fix locking of critical sections

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Date:   Wed, 17 Mar 2021 17:27:38 +0000
From:   "Laba, SlawomirX" <slawomirx.laba@...el.com>
To:     Stefan Assmann <sassmann@...nic.de>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        Jakub Kicinski <kuba@...nel.org>
CC:     "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "Yang, Lihong" <lihong.yang@...el.com>,
        "Nunley, Nicholas D" <nicholas.d.nunley@...el.com>
Subject: RE: [PATCH] iavf: fix locking of critical sections

We were discussing introducing mutexes in those critical spots for a long time now (in my team).
Stefan, if you find time, you are most welcome to offer your solution with mutexes.

Slawek


-----Original Message-----
From: Stefan Assmann <sassmann@...nic.de> 
Sent: Wednesday, March 17, 2021 8:50 AM
To: Brandeburg, Jesse <jesse.brandeburg@...el.com>; Jakub Kicinski <kuba@...nel.org>
Cc: intel-wired-lan@...ts.osuosl.org; netdev@...r.kernel.org; Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Yang, Lihong <lihong.yang@...el.com>; Laba, SlawomirX <slawomirx.laba@...el.com>; Nunley, Nicholas D <nicholas.d.nunley@...el.com>
Subject: Re: [PATCH] iavf: fix locking of critical sections

On 16.03.21 23:02, Jesse Brandeburg wrote:
> Jakub Kicinski wrote:
>>>> I personally think that the overuse of flags in Intel drivers 
>>>> brings nothing but trouble. At which point does it make sense to 
>>>> just add a lock / semaphore here rather than open code all this 
>>>> with no clear semantics? No code seems to just test the 
>>>> __IAVF_IN_CRITICAL_TASK flag, all the uses look like poor man's 
>>>> locking at a quick grep. What am I missing?
>>>
>>> I agree with you that the locking could be done with other locking 
>>> mechanisms just as good. I didn't invent the current method so I'll 
>>> let Intel comment on that part, but I'd like to point out that what 
>>> I'm making use of is fixing what is currently in the driver.
>>
>> Right, I should have made it clear that I don't blame you for the 
>> current state of things. Would you mind sending a patch on top of 
>> this one to do a conversion to a semaphore?

Sure, I'm happy to help working on the conversion once the current issue is resolved.

>> Intel folks any opinions?
> 
> I know Slawomir has been working closely with Stefan on figuring out 
> the right ways to fix this code.  Hopefully he can speak for himself, 
> but I know he's on Europe time.
> 
> As for conversion to mutexes I'm a big fan, and as long as we don't 
> have too many collisions with the RTNL lock I think it's a reasonable 
> improvement to do, and if Stefan doesn't want to work on it, we can 
> look into whether Slawomir or his team can.

I'd appreciate to be involved.
Thanks!

  Stefan