From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: Johannes Berg <johannes@sipsolutions.net>, linux-um@lists.infradead.org
Cc: richard@nod.at
Subject: Re: [PATCH v5] um: Enable preemption in UML
Date: Fri, 22 Sep 2023 09:01:54 +0100 [thread overview]
Message-ID: <28f0be57-829b-9ddf-7b0d-a6c84932cbda@cambridgegreys.com> (raw)
In-Reply-To: <2de07f54b33dc060b75d982d4d8189f12e0d4c45.camel@sipsolutions.net>
On 22/09/2023 08:40, Johannes Berg wrote:
> On Fri, 2023-09-22 at 08:38 +0100, Anton Ivanov wrote:
>>> I had enabled CONFIG_DEBUG_ATOMIC_SLEEP because that's actually
>>> something I'd really like to have in our testing.
>>>
>>> But with that issue I don't even know how we get there really. It
>>> doesn't even happen every time we fork?
>>>
>>> I'll dig a little bit, but did you try enabling
>>> CONFIG_DEBUG_ATOMIC_SLEEP also?
>> Will do. I have no crashes over here so I need to trigger this one first.
>>
>> Though, frankly, if it is a race in a tlb flush it may be subject to local conditions. So it will be difficult to reproduce.
>>
> Yes, it might be a race in the fork handler maybe? IOW, whenever we
> actually do fork, it depends on what conditions the rest is in? I'm not
> sure I fully figured out right now how the fork handler is doing all
> this, but I sent my mail before I could since you were discussing :)
>
> But it shouldn't be impossible - while I don't see it for every fork, it
> does happen 8 or 9 times in a very simple test that just boots, pings a
> bit, and then shuts down, so ...
My favorite test which I run on all changes is:
find /usr -type f -exec cat {} > /dev/null \;
On Debian this forks /bin/cat for each file and does IO on it. That test passes here every time :(
However, I did not have debug turned on. So, I would not be surprised if something in the debug
portion of the config makes the crashes more likely.
Otherwise, each fork is a forced tlb_flush_all, so it is a massive tlb exercise. Any bugs, locking, etc are likely to show up.
>
> johannes
>
--
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/
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next prev parent reply other threads:[~2023-09-22 8:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-22 6:52 [PATCH v5] um: Enable preemption in UML anton.ivanov
2023-09-22 7:27 ` Richard Weinberger
2023-09-22 7:29 ` Anton Ivanov
2023-09-22 7:30 ` Johannes Berg
2023-09-22 7:38 ` Anton Ivanov
2023-09-22 7:40 ` Johannes Berg
2023-09-22 8:01 ` Anton Ivanov [this message]
2023-09-22 8:13 ` Johannes Berg
2023-09-22 8:40 ` Anton Ivanov
2023-09-22 8:41 ` Johannes Berg
2023-09-22 8:43 ` Johannes Berg
2023-09-22 9:04 ` Johannes Berg
2023-09-22 9:12 ` Anton Ivanov
2023-09-22 9:06 ` Anton Ivanov
2023-09-22 9:10 ` Johannes Berg
2023-09-22 9:14 ` Johannes Berg
2023-09-22 9:19 ` Anton Ivanov
2023-09-22 9:51 ` Johannes Berg
2023-09-22 9:55 ` Johannes Berg
2023-09-22 10:55 ` Anton Ivanov
2023-09-22 11:17 ` Johannes Berg
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