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Date:      Mon, 9 Nov 2020 13:28:13 +0200
From:      Andriy Gapon <avg@FreeBSD.org>
To:        Mateusz Guzik <mjguzik@gmail.com>
Cc:        freebsd-current@freebsd.org, freebsd-fs@freebsd.org
Subject:   Re: panic: VERIFY(ZFS_TEARDOWN_READ_HELD(zfsvfs)) failed
Message-ID:  <5850cf84-4004-3782-45cb-bf4ed6d71b1b@FreeBSD.org>
In-Reply-To: <CAGudoHEj9jXA-q4x0sxRoTZBaog1gfs9YCTAjSezWkS3q3DfKw@mail.gmail.com>
References:  <98c87b4f-4327-8a19-cf51-f3a14e42edf4@FreeBSD.org> <CAGudoHHmBW64HsKq8h8y4_8e9WMqpFgzx2XikpcRCz9=EmRwEQ@mail.gmail.com> <bbeabc54-7b1d-e617-65be-9fc842b53824@FreeBSD.org> <CAGudoHHEJj0x1tecy%2Bd-HgkVgc3rRb5%2BhgRT_jW%2Bx2PEnu7o-w@mail.gmail.com> <CAGudoHHsghUQODipQ7dO3i-jNn1%2BYQza0XTqLBEd4N9nxneLDA@mail.gmail.com> <CAGudoHEj9jXA-q4x0sxRoTZBaog1gfs9YCTAjSezWkS3q3DfKw@mail.gmail.com>

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On 07/11/2020 19:00, Mateusz Guzik wrote:
> Fixed as of r367454 (also see r367453).

Thank you!

> On 11/6/20, Mateusz Guzik <mjguzik@gmail.com> wrote:
>> I think I have an idea how to keep this. In the meantime you can just
>> comment it out.
>>
>> On 11/6/20, Mateusz Guzik <mjguzik@gmail.com> wrote:
>>> On 11/6/20, Andriy Gapon <avg@freebsd.org> wrote:
>>>> On 06/11/2020 22:58, Mateusz Guzik wrote:
>>>>> Note the underlying primitive was recently replaced.
>>>>>
>>>>> One immediate thing to check would be exact state of the lock.
>>>>> READ_HELD checks for reading only, fails if you have this
>>>>> write-locked, which is a plausible explanation if you are coming in
>>>>> from less likely codepath.
>>>>>
>>>>> iow what's the backtrace and can you print both rms->readers and
>>>>> rms->owner (+ curthread)
>>>>
>>>> Unfortunately, I do not have a vmcore, only a picture of the screen.
>>>>
>>>> ZFS code looks correct, the lock should be held in read mode, so indeed
>>>> I
>>>> suspect that the problem is with rms.
>>>>
>>>> It looks like rms_rlock() does not change rmslock::readers, but
>>>> rms_rowned()
>>>> checks it?
>>>>
>>>> That's just from a first, super-quick look at the code.
>>>>
>>>
>>> Heh, now that you mention it, I remember wanting to just remove the
>>> arguably spurious assert. Linux is never doing it for reading. The
>>> only state asserts made are for writing which works fine.
>>>
>>> As for reading assertions, there is no performant way to make it work
>>> and I don't think it is worth it as it is.
>>>
>>> As such, I vote for just removing these 2 asserts. They really don't
>>> buy anything to begin with.
>>>
>>> --
>>> Mateusz Guzik <mjguzik gmail.com>
>>>
>>
>>
>> --
>> Mateusz Guzik <mjguzik gmail.com>
>>
> 
> 


-- 
Andriy Gapon



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