linux-kernel - Re: [4.10, panic, regression] iscsi: null pointer deref at iscsi_tcp_segment

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Date:   Thu, 22 Dec 2016 21:20:32 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Dave Chinner <david@...morbit.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Anvin <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [4.10, panic, regression] iscsi: null pointer deref at
 iscsi_tcp_segment_done+0x20d/0x2e0

On Thu, 22 Dec 2016, Linus Torvalds wrote:
> On Wed, Dec 21, 2016 at 10:28 PM, Dave Chinner <david@...morbit.com> wrote:
> >
> > This sort of thing is normally indicative of a memory reclaim or
> > lock contention problem. Profile showed unusual spinlock contention,
> > but then I realised there was only one kswapd thread running.
> > Yup, sure enough, it's caused by a major change in memory reclaim
> > behaviour:
> >
> > [    0.000000] Zone ranges:
> > [    0.000000]   DMA      [mem 0x0000000000001000-0x0000000000ffffff]
> > [    0.000000]   DMA32    [mem 0x0000000001000000-0x00000000ffffffff]
> > [    0.000000]   Normal   [mem 0x0000000100000000-0x000000083fffffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000000001000-0x000000000009efff]
> > [    0.000000]   node   0: [mem 0x0000000000100000-0x00000000bffdefff]
> > [    0.000000]   node   0: [mem 0x0000000100000000-0x00000003bfffffff]
> > [    0.000000]   node   0: [mem 0x00000005c0000000-0x00000005ffffffff]
> > [    0.000000]   node   0: [mem 0x0000000800000000-0x000000083fffffff]
> > [    0.000000] Initmem setup node 0 [mem 0x0000000000001000-0x000000083fffffff]
> >
> > the numa=fake=4 CLI option is broken.
> 
> Ok, I think that is independent of anything else. Removing block
> people and adding the x86 people.
> 
> I'm not seeing anything at all that would change the fake numa stuff,
> but maybe the cpu hotplug changes?

Nope. Double checked it for correctness. The cpu hotplug code there is not
involved in setting up kswapd threads. They are created by the memory node
stuff.

> Thomas/Ingo/Peter - Dave is going away for several months, so you
> won't get feedback from him, but can you look at this? Or maybe point
> me towards the right people - I'm seeing no possible relevant changes
> at all fir x85 numa since 4.9, so it must be some indirect breakage.
> 
> Dave is using fake-numa to do performance testing in a VM, and it's a
> big deal for the node optimizations for writeback etc. Do you have any
> ideas?

There was the nodeid -> cpuid mapping stuff, but that was in 4.9 so it's
not a post 4.9 wreckage, but maybe it's related nevertheless.

> Dave, if you're still around, can you send out the kernel config file
> you used...

Config file and kernel command line would be helpful.

Thanks,

	tglx