Message-ID: <MW4PR14MB479687DDEC1EB0C4AA5F5CF1A1A39@MW4PR14MB4796.namprd14.prod.outlook.com>
Date:   Thu, 23 Sep 2021 15:17:26 +0000
From:   PJ Waskiewicz <pwaskiewicz@...ptrading.com>
To:     "Dziedziuch, SylwesterX" <sylwesterx.dziedziuch@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "pjwaskiewicz@...il.com" <pjwaskiewicz@...il.com>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "Machnikowski, Maciej" <maciej.machnikowski@...el.com>
Subject: RE: [PATCH 1/1] i40e: Avoid double IRQ free on error path in probe()

> > Hello PJ,
>
> Hello,

Hi Tony and Sylwester,

Any updates/comments on my reply from a few days ago on this?

-PJ

> >
> > > static void i40e_free_misc_vector(struct i40e_pf *pf) {
> > >         /* Disable ICR 0 */
> > >         wr32(&pf->hw, I40E_PFINT_ICR0_ENA, 0);
> > >         i40e_flush(&pf->hw);
> > >
> > > Would you still want to do that blindly if the vector wasn't
> > > allocated in the first place?  Seems excessive, but it'd be
> > > harmless.  Seems like not calling this function altogether would be
> > > cleaner and generate less MMIO activity if the MISC vector wasn't
> > > allocated at all and
> > we're falling out of an error path...
> > >
> > > I am really at a loss here.  This is clearly broken.  We have an Oops.
> > > We get these occasionally on boot, and it's really annoying to deal
> > > with on production machines.  What is the definition of "soon" here
> > > for this new patch to show up?  My distro vendor would love to pull
> > > some sort of fix in so we can get it into our build images, and stop
> > > having this problem.  My patch fixes the immediate problem.  If you
> > > don't like the patch (which it appears you don't; that's fine), then
> > > stalling or saying a different fix is coming "soon" is really not a
> > > great support model.  This would be great to merge, and then if you
> > > want to make it "better" on your schedule, it's open source, and you
> > > can submit a patch.  Or I'll be happy to respin the patch, but still
> > > calling free_misc_vector() in an error path when the MISC vector was
> > never allocated seems like a bad design decision to me.
> > >
> > > -PJ
> >
> > I totally agree that we shouldn’t call free_misc_vector if misc vector
> > wasn't allocated yet but to me this is not what your patch is doing.
> > free_misc_vector() is called in clear_interrupt_scheme not
> > reset_interrupt_capability(). In your patch clear_interrupt_scheme()
> > will still be called when pf switch setup fails in i40e_probe() and it
> > will still call free_misc_vector on unallocated misc IRQ. Other proper
> > way to fix this would be moving free_misc_vector() out of
> > clear_interrupt_scheme() and calling it separately when misc vector
> > was really allocated. As for the hw register being written in our
> > patch as you said it's harmless. The patch we've prepared should be on iwl
> today.
> >
>
> Ok, I see the patch on IWL....let's discuss....
>
> Just above, I pointed out that if the MISC vector hasn't been allocated at all,
> then we don't want to call free_misc_vector() at all.  That would also mean
> the suggestion to check the atomic state bit to avoid the actual free would
> *still* have the code call free_misc_vector(), and only skip the actual free
> (after doing an unnecessary MMIO write and then read to flush).  I pointed
> out that wouldn't be ideal, and you, just above, agreed.  Yet, the fix you guys
> submitted to IWL does exactly that.  So are we just saying things to bury this
> thread and hope it goes away, or just willfully not doing what we agreed on?
> It's pretty disheartening to consider feedback, agree to it, then completely
> ignore it.  That's not how open source works...
>
> Also, regardless how you guys want the code to work, it's usually good form
> to include a "Reported-by:" in a patch if you're deciding not to take a
> proposed patch.  It's even better form to include the Oops that was reported
> in the first patch, since that makes things like ${SEARCH_ENGINE} work for
> people running into the same issue have a chance to find a solution.  Not
> doing either of these when someone else has done work to identify an issue,
> test a fix, and propose it, is not a good way to attract more people to work on
> this driver in the future.
>
> If we wanted to do something where free_misc_vector() isn't called if the
> state flag isn't set, then why not something like this, which would keep in the
> spirit of what we agreed on above:
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c
> b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 1d1f52756a93..a40193bcc7b7 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -4868,7 +4868,9 @@ static void i40e_clear_interrupt_scheme(struct
> i40e_pf *pf)  {
>         int i;
>
> -       i40e_free_misc_vector(pf);
> +       /* Only attempt to free the misc vector if it's already allocated */
> +       if (test_bit(__I40E_MISC_IRQ_REQUESTED, pf->state))
> +               i40e_free_misc_vector(pf);
>
>         i40e_put_lump(pf->irq_pile, pf->iwarp_base_vector,
>                       I40E_IWARP_IRQ_PILE_ID);
>
> -PJ

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