linux-kernel - Re: [BUG] seltests/iommu: runaway ./iommufd consuming 99% CPU after a failed assert()

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Message-ID: <20240327114029.GC946323@nvidia.com>
Date: Wed, 27 Mar 2024 08:40:29 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Joao Martins <joao.m.martins@...cle.com>
Cc: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>, iommu@...ts.linux.dev,
	Kevin Tian <kevin.tian@...el.com>, Shuah Khan <shuah@...nel.org>,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] seltests/iommu: runaway ./iommufd consuming 99% CPU after
 a failed assert()

On Wed, Mar 27, 2024 at 10:41:52AM +0000, Joao Martins wrote:
> On 25/03/2024 13:52, Jason Gunthorpe wrote:
> > On Mon, Mar 25, 2024 at 12:17:28PM +0000, Joao Martins wrote:
> >>> However, I am not smart enough to figure out why ...
> >>>
> >>> Apparently, from the source, mmap() fails to allocate pages on the desired address:
> >>>
> >>>   1746         assert((uintptr_t)self->buffer % HUGEPAGE_SIZE == 0);
> >>>   1747         vrc = mmap(self->buffer, variant->buffer_size, PROT_READ |
> >>> PROT_WRITE,
> >>>   1748                    mmap_flags, -1, 0);
> >>> → 1749         assert(vrc == self->buffer);
> >>>   1750
> >>>
> >>> But I am not that deep into the source to figure our what was intended and what
> >>> went
> >>> wrong :-/
> >>
> >> I can SKIP() the test rather assert() in here if it helps. Though there are
> >> other tests that fail if no hugetlb pages are reserved.
> >>
> >> But I am not sure if this is problem here as the initial bug email had an
> >> enterily different set of failures? Maybe all you need is an assert() and it
> >> gets into this state?
> > 
> > I feel like there is something wrong with the kselftest framework,
> > there should be some way to fail the setup/teardown operations without
> > triggering an infinite loop :(
> 
> I am now wondering if the problem is the fact that we have an assert() in the
> middle of FIXTURE_{TEST,SETUP} whereby we should be having ASSERT_TRUE() (or any
> other kselftest macro that). The expect/assert macros from kselftest() don't do
> asserts and it looks like we are failing mid tests in the assert().

Those ASSERT_TRUE cause infinite loops when used within the setup
context, I removed them and switched to assert because of this - which
did work OK in my testing at least.

Jason