RE: [PATCH 1/1] i40e: Avoid double IRQ free on error path in probe()

[PJ Waskiewicz <pwaskiewicz@jumptrading.com>]

Hi Sylwester,

> -----Original Message-----
> From: Dziedziuch, SylwesterX <sylwesterx.dziedziuch@intel.com>
> Sent: Tuesday, September 14, 2021 1:24 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; PJ Waskiewicz
> <pwaskiewicz@jumptrading.com>
> Cc: davem@davemloft.net; pjwaskiewicz@gmail.com; Fijalkowski, Maciej
> <maciej.fijalkowski@intel.com>; Loktionov, Aleksandr
> <aleksandr.loktionov@intel.com>; netdev@vger.kernel.org; Brandeburg,
> Jesse <jesse.brandeburg@intel.com>; intel-wired-lan@lists.osuosl.org
> Subject: RE: [PATCH 1/1] i40e: Avoid double IRQ free on error path in probe()
>

[snip]

> > > It's been 2 weeks since I replied.  Any update on this?  Maciej had
> > > already reviewed the patch, so hoping we can just move along with
> > > it, or get something else out soon?
> > >
> > > I'd really like this to not just fall into a void waiting for a
> > > different patch when this fixes the issue.
> >
> > Hi PJ,
> >
> > I haven't seen a recent update on this. I'm asking for an update.
> > Otherwise, Alex and Sylwester are on this thread; perhaps they have
> > some info.
> >
> > Thanks,
> > Tony
> >
>
> Hello,
>
> The driver does not blindly try to free MSI-X vector twice here. This is
> guarded by I40E_FLAG_MSIX_ENABLED and I40E_FLAG_MSI_ENABLED flags.
> Only if those flags are set we will try to free MSI/MSI-X vectors in
> i40e_reset_interrupt_capability(). Additionally
> i40e_reset_interrupt_capability() clears those flags every time it is called so
> even if we call it twice in a row the driver will not free the vectors twice. I
> really can't see how this patch is fixing anything as the issue here is not with
> MSI vectors but with misc IRQ vectors. We have a proper patch for this ready
> in OOT and we will upstream it soon. The problem here is that in
> i40e_clear_interrupt_scheme() driver calls i40e_free_misc_vector() but in
> case VSI setup fails misc vector is not allocated yet and we get a call trace in
> free_irq that we are trying to free IRQ that has not been allocated yet.

That's fine.  I do see the guards for the queue vectors.  I saw them before.  The point is i40e_clear_interrupt_scheme() tries to free the MISC vector without guard, or without any check if it was allocated before.  In the error path, it tries to free it.  We get an oops for a double-free of an IRQ (also read: free an unallocated interrupt).

I know how this code works.  I wrote the original reset/clear interrupt scheme functions in ixgbe, and ported them to i40e when I wrote the initial driver.  We hit a problem in production, and I'm trying to patch it where we don't need to call clear_interrupt_scheme() if we fail to bring the main VSI online during probe.  I don't see why this needs to be a semantic discussion over how the vectors are freed.  We have a valid oops, still have it upstream.

I've also checked the OOT driver on SourceForge released in July.  It has the same problem:

static void i40e_clear_interrupt_scheme(struct i40e_pf *pf)
{
        int i;

        i40e_free_misc_vector(pf);

        i40e_put_lump(pf->irq_pile, pf->iwarp_base_vector,
                      I40E_IWARP_IRQ_PILE_ID);
[...]

I've also been told by some friends that no fix exists in internal git either.  So please, either propose a fix, ask me to change the patch, or merge it.  I'd really like to have our OS vendor be able to pick up this fix asap once it hits an upstream tree.

Cheers,
-PJ Waskiewicz

> Regards
> Sylwester Dziedziuch
>
> > > -PJ
> > >
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