netdev - Re: [patch net-next v3 01/11] net: devlink: make sure that devlink_try_get() works with valid pointer during xarray iteration

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Message-ID: <Yt5RjrqG1WZelSOH@nanopsycho>
Date:   Mon, 25 Jul 2022 10:17:18 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, idosch@...dia.com,
        petrm@...dia.com, pabeni@...hat.com, edumazet@...gle.com,
        mlxsw@...dia.com, saeedm@...dia.com, snelson@...sando.io
Subject: Re: [patch net-next v3 01/11] net: devlink: make sure that
 devlink_try_get() works with valid pointer during xarray iteration

Sat, Jul 23, 2022 at 05:41:08PM CEST, jiri@...nulli.us wrote:
>Fri, Jul 22, 2022 at 08:23:48PM CEST, kuba@...nel.org wrote:
>>On Fri, 22 Jul 2022 17:50:17 +0200 Jiri Pirko wrote:
>>> >Plus we need to be more careful about the unregistering order, I
>>> >believe the correct ordering is:
>>> >
>>> >	clear_unmark()
>>> >	put()
>>> >	wait()
>>> >	notify()
>>> >
>>> >but I believe we'll run afoul of Leon's notification suppression.
>>> >So I guess notify() has to go before clear_unmark(), but we should
>>> >unmark before we wait otherwise we could live lock (once the mutex 
>>> >is really gone, I mean).  
>>> 
>>> Kuba, could you elaborate a bit more about the live lock problem here?
>>
>>Once the devlink_mutex lock is gone - (unprivileged) user space dumping
>>devlink objects could prevent any de-registration from happening
>>because it can keep the reference of the instance up. So we should mark
>>the instance as not REGISTERED first, then go to wait.
>
>Yeah, that is what I thought. I resolved it as you wrote. I removed the
>WARN_ON from devlink_notify(). It is really not good for anything
>anyway.

The check for "registered" is in more notifications. I will handle this
in the next patchset, you are right, it is not needed to handle here.

Sending v4.

Thanks!

>
>
>>
>>Pretty theoretical, I guess, but I wanted to mention it in case you can
>>figure out a solution along the way :S I don't think it's a blocker
>>right now since we still have the mutex.
>
>Got it.