Re: uml segfault during I/O

From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: rrs@researchut.com, linux-um@lists.infradead.org
Subject: Re: uml segfault during I/O
Date: Thu, 17 Oct 2019 17:29:21 +0100	[thread overview]
Message-ID: <4892b3ca-6b26-0b96-d21f-ac8b31fb2270@cambridgegreys.com> (raw)
In-Reply-To: <c7135e15-d2e4-3bce-9584-9032ddca72fe@cambridgegreys.com>

On 17/10/2019 16:03, Anton Ivanov wrote:
> 
> 
> On 17/10/2019 14:33, Anton Ivanov wrote:
>>
>>
>> On 17/10/2019 14:30, Ritesh Raj Sarraf wrote:
>>> On Thu, 2019-10-17 at 14:02 +0100, Anton Ivanov wrote:
>>>> Looking into that. I have not run into anything like that, but I have
>>>> not used any of the legacy networking for 5 odd years now.
>>>>
>>>
>>> Do you think this is related to networking ? I ask because there was no
>>> network activity going on.
>>
>> no, it's disk somewhere. I managed to reproduce it with 5.2 stock on 
>> Debian 5.2 host.
>>
>>>
>>> apt is just an example. The packages were all already downloaded and
>>> there was no network activity. Rather, there was block I/O.
>>
>> I am looking into that.
>>
>>>
>>> One thing I noticed, which may or may not be useful to this report. I
>>> was booting the uml guest and immediately logging into it and running
>>> the block I/O. And the segfault would occur.
>>>
>>> If I, instead, booted the uml vm and let it remain idle for a minute or
>>> so and then did the I/O, it worked fine. So I am not sure if there is
>>> any lazy initialization happening in the background which gets
>>> corrupted during immediate hot boot I/O.
>>
>> Interesting...
>>
>>>
>>> On the other hand, if you think there can be any number of commands to
>>> run locally that could generate more information, please assist me so.
>>
>> As I said - I managed to reproduce it, I am looking at it. In first 
>> instance I am trying with a couple of version up/down to see if this 
>> is 5.2 specific.
> 
> I cannot even get it to start on 5.4-rc1, 5.3 shows the same symptoms.

This is something outside the UBD driver as such. There were no notable 
changes to it since we ported it to block-mq and added DISCARD which was 
quite a while back.

I am going to check the other usual suspects such as IRQs, but that is 
something I test quite extensively when working on the networking side.

So I suspect that this is something outside UML which is showing only in 
UML for some reason.

A.

> 
>>
>>>
>>> Thanks,
>>> Ritesh
>>>
>>>
>>> _______________________________________________
>>> linux-um mailing list
>>> linux-um@lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-um
>>>
>>
> 

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/

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