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

Hello PJ,

Sorry for the late response. I am applying your suggestions to the patch. The updated version will be on IWL in a moment.

-----Original Message-----
From: PJ Waskiewicz <redacted>
Sent: Thursday, September 23, 2021 5:17 PM
To: Dziedziuch, SylwesterX <redacted>; Nguyen,
Anthony L [off-list ref]
Cc: davem@davemloft.net; <redacted>; Fijalkowski, Maciej
[off-list ref]; Loktionov, Aleksandr
[off-list ref]; netdev@vger.kernel.org; Brandeburg, Jesse
[off-list ref]; intel-wired-lan@lists.osuosl.org;
Machnikowski, Maciej [off-list ref]
Subject: RE: [PATCH 1/1] i40e: Avoid double IRQ free on error path in probe()

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Hello PJ,

Hello,

Hi Tony and Sylwester,

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

-PJ

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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...

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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.

quoted

-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.

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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?

quoted

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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