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

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Message-ID: <20210316132905.5d0f90dd@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 16 Mar 2021 13:29:05 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Stefan Assmann <sassmann@...nic.de>
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        anthony.l.nguyen@...el.com, lihong.yang@...el.com,
        jesse.brandeburg@...el.com, slawomirx.laba@...el.com,
        nicholas.d.nunley@...el.com
Subject: Re: [PATCH] iavf: fix locking of critical sections

On Tue, 16 Mar 2021 18:27:10 +0100 Stefan Assmann wrote:
> On 16.03.21 18:14, Jakub Kicinski wrote:
> > On Tue, 16 Mar 2021 11:01:41 +0100 Stefan Assmann wrote:  
> >> To avoid races between iavf_init_task(), iavf_reset_task(),
> >> iavf_watchdog_task(), iavf_adminq_task() as well as the shutdown and
> >> remove functions more locking is required.
> >> The current protection by __IAVF_IN_CRITICAL_TASK is needed in
> >> additional places.
> >>
> >> - The reset task performs state transitions, therefore needs locking.
> >> - The adminq task acts on replies from the PF in
> >>   iavf_virtchnl_completion() which may alter the states.
> >> - The init task is not only run during probe but also if a VF gets stuck
> >>   to reinitialize it.
> >> - The shutdown function performs a state transition.
> >> - The remove function perorms a state transition and also free's
> >>   resources.
> >>
> >> iavf_lock_timeout() is introduced to avoid waiting infinitely
> >> and cause a deadlock. Rather unlock and print a warning.
> >>
> >> Signed-off-by: Stefan Assmann <sassmann@...nic.de>  
> > 
> > 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? 

Intel folks any opinions?