linux-kernel - Re: [PATCH v1] selftests/mm: fix charge_reserved

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Message-ID: <95a7dbfe-d88f-4d8b-898e-87c18e7d5813@redhat.com>
Date: Wed, 21 Aug 2024 18:04:40 +0200
From: David Hildenbrand <david@...hat.com>
To: Mina Almasry <almasrymina@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, Mario Casquero <mcasquer@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>,
 Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH v1] selftests/mm: fix charge_reserved_hugetlb.sh test

On 21.08.24 17:59, Mina Almasry wrote:
> On Wed, Aug 21, 2024 at 8:31 AM David Hildenbrand <david@...hat.com> wrote:
>>
>> Currently, running the charge_reserved_hugetlb.sh selftest we can
>> sometimes observe something like:
>>
>>    $ ./charge_reserved_hugetlb.sh -cgroup-v2
>>    ...
>>    write_result is 0
>>    After write:
>>    hugetlb_usage=0
>>    reserved_usage=10485760
>>    killing write_to_hugetlbfs
>>    Received 2.
>>    Deleting the memory
>>    Detach failure: Invalid argument
>>    umount: /mnt/huge: target is busy.
>>
>> Both cases are issues in the test.
>>
>> While the unmount error seems to be racy, it will make the test fail:
>>          $ ./run_vmtests.sh -t hugetlb
>>          ...
>>          # [FAIL]
>>          not ok 10 charge_reserved_hugetlb.sh -cgroup-v2 # exit=32
>>
>> The issue is that we are not waiting for the write_to_hugetlbfs process
>> to quit. So it might still have a hugetlbfs file open, about which
>> umount is not happy. Fix that by making "killall" wait for the process
>> to quit.
>>
>> The other error ("Detach failure: Invalid argument") does not seem to
>> result in a test error, but is misleading. Turns out write_to_hugetlbfs.c
>> unconditionally tries to cleanup using shmdt(), even when we only
>> mmap()'ed a hugetlb file. Even worse, shmaddr is never even set for the
>> SHM case. Fix that as well.
>>
>> With this change it seems to work as expected.
>>
>> Fixes: 29750f71a9b4 ("hugetlb_cgroup: add hugetlb_cgroup reservation tests")
>> Reported-by: Mario Casquero <mcasquer@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Shuah Khan <shuah@...nel.org>
>> Cc: Muchun Song <muchun.song@...ux.dev>
>> Cc: Mina Almasry <almasrymina@...gle.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> Initially I thought it could be nice to split fixes for the 2 issues
> in separate patches in case one of them ends up needing a revert or
> something, but probably not worth a respin. Fixes look good to me.

I was debating with myself as well if it should be separated, but 
decided to go the simple route of a single patch :)

> 
> Reviewed-by: Mina Almasry <almasrymina@...gle.com>

Thanks!

-- 
Cheers,

David / dhildenb