Subject: Re: 4.4: INFO: rcu_sched self-detected stall on CPU
To: Steven Haigh <netwiz@crc.id.au>,
        xen-devel <xen-devel@lists.xenproject.org>,
        linux-kernel@vger.kernel.org
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Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <56FBD851.9030608@oracle.com>
Date: Wed, 30 Mar 2016 09:44:49 -0400
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On 03/29/2016 02:04 PM, Steven Haigh wrote:
> Greg, please see below - this is probably more for you...
>
> On 03/29/2016 04:56 AM, Steven Haigh wrote:
>> Interestingly enough, this just happened again - but on a different
>> virtual machine. I'm starting to wonder if this may have something to do
>> with the uptime of the machine - as the system that this seems to happen
>> to is always different.
>>
>> Destroying it and monitoring it again has so far come up blank.
>>
>> I've thrown the latest lot of kernel messages here:
>>       http://paste.fedoraproject.org/346802/59241532
> So I just did a bit of digging via the almighty Google.
>
> I started hunting for these lines, as they happen just before the stall:
> BUG: Bad rss-counter state mm:ffff88007b7db480 idx:2 val:-1
> BUG: Bad rss-counter state mm:ffff880079c638c0 idx:0 val:-1
> BUG: Bad rss-counter state mm:ffff880079c638c0 idx:2 val:-1
>
> I stumbled across this post on the lkml:
>      http://marc.info/?l=linux-kernel&m=145141546409607
>
> The patch attached seems to reference the following change in
> unmap_mapping_range in mm/memory.c:
>> -	struct zap_details details;
>> +	struct zap_details details = { };
> When I browse the GIT tree for 4.4.6:
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/mm/memory.c?id=refs/tags/v4.4.6
>
> I see at line 2411:
> struct zap_details details;
>
> Is this something that has been missed being merged into the 4.4 tree?
> I'll admit my kernel knowledge is not enough to understand what the code
> actually does - but the similarities here seem uncanny.


The patch that you are referring to is trying to fix a bug in a feature 
that's not in the mainline yet ("mm, oom: introduce oom reaper").

-boris