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

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Date: Wed, 27 Mar 2024 15:04:09 +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 27/03/2024 11:40, Jason Gunthorpe wrote:
> 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.

Strange because we make use of ASSERT* widely in our selftests fixture-setup.

setup_sizes() is run before the tests so it can't use ASSERT macros for sure;
maybe that's what you refer?