Message-ID: <MW4PR14MB47967810D43031FF8C4C2265A1A19@MW4PR14MB4796.namprd14.prod.outlook.com>
Date:   Tue, 21 Sep 2021 17:06:48 +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,

>
> > 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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