linux-kernel - RE: [PATCH] iommufd/selftest: Fix dirty

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Date:   Fri, 17 Nov 2023 03:15:25 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Robin Murphy <robin.murphy@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] iommufd/selftest: Fix dirty_bitmap tests

> From: Robin Murphy <robin.murphy@....com>
> Sent: Friday, November 17, 2023 1:44 AM
> 
> On 16/11/2023 5:28 pm, Joao Martins wrote:
> > On 16/11/2023 16:52, Robin Murphy wrote:
> >> The ASSERT_EQ() macro sneakily expands to two statements, so the loop
> >> here needs braces to ensure it captures both and actually terminates the
> >> test upon failure.
> >
> > Ugh
> >
> >> Where these tests are currently failing on my arm64
> >> machine, this reduces the number of logged lines from a rather
> >> unreasonable ~197,000 down to 10. While we're at it, we can also clean
> >> up the tautologous "count" calculations whose assertions can never fail
> >> unless mathematics and/or the C language become fundamentally broken.
> >>
> >> Fixes: a9af47e382a4 ("iommufd/selftest: Test
> IOMMU_HWPT_GET_DIRTY_BITMAP")
> >> Signed-off-by: Robin Murphy <robin.murphy@....com>
> >
> > I was going to say that the second assert is useful, but we are already test
> the
> > number of bits we set against what the mock domain set after
> > mock_domain_set_dirty(). So the second is redundantly testing the same,
> and can
> > be removed as you are doing. Thanks for fixing this.
> 
> Yeah, it's still effectively just counting half the number of loop
> iterations executed, but since there's no control flow that could exit
> the loop early and still reach the assertion, it must always be true
> following the previous assertion that out_dirty == nr == nbits/2.
> 
> > I would suggest the subject to:
> >
> > 	iommufd/selftest: Fix _test_mock_dirty_bitmaps()
> >
> > Because dirty-bitmap tests seems to imply the whole fixture, which covers
> more
> > than the bitmaps.
> 
> Sure, that sounds reasonable. Jason, Kevin, would you want a v2 for that
> or could it be fixed up when applying?
> 

Jason can help fix it when applying.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>