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

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Message-ID: <f8e03425-98cf-4076-8959-d85eda846bab@oracle.com>
Date: Wed, 27 Mar 2024 10:41:52 +0000
From: Joao Martins <joao.m.martins@...cle.com>
To: Jason Gunthorpe <jgg@...dia.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 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().

Maybe it is OK for setup_sizes(), but maybe not OK for the rest (i.e. during the
actual setup / tests). I can throw a patch there to see if this helps Mirsad.