linux-kernel - Re: 4.4: INFO: rcu_sched self-detected stall on CPU

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Message-ID: <56FAC3AC.9050802@crc.id.au>
Date:	Wed, 30 Mar 2016 05:04:28 +1100
From:	Steven Haigh <netwiz@....id.au>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	linux-kernel@...r.kernel.org
Cc:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: 4.4: INFO: rcu_sched self-detected stall on CPU

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.

-- 
Steven Haigh

Email: netwiz@....id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897



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