Date:   Fri, 23 Dec 2016 08:06:07 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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 Fri, Dec 23, 2016 at 07:42:40AM +1100, Dave Chinner wrote:
> On Thu, Dec 22, 2016 at 09:24:12AM -0800, 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?
> > 
> > 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?
> > 
> > Dave, if you're still around, can you send out the kernel config file
> > you used...
> 
> Looking at this fresh this morning (i.e. not pissed off by having
> everything I tried to do fail in different ways all afternoon) I
> found this:
> 
> $ grep NUMA .config
> CONFIG_ARCH_SUPPORTS_NUMA_BALANCING=y
> # CONFIG_NUMA is not set
> $
> 
> The .config I was using for 4.9 got 'make oldconfig' upgraded, and
> looking at it there's a bunch of stuff that has been turned off that
> I know was set:
> 
> # CONFIG_EXPERT is not set
> # CONFIG_PARAVIRT_SPINLOCKS is not set
> # CONFIG_COMPACTION is not set
> 
> and stuff I never use so don't set was set, like kernel crash dump,
> a bunch of stuff for AMD CPUs, susp/resume and power management
> debug, every partition type and filesystem under the sun was
> selected, heaps of network devices enabled, etc.
> 
> So it looks like the problem has occurred during oldconfig, meaning
> I have no idea exactly WTF I was testing. Rebuilding now with a
> saner config, see what happens.

Better, but still bad. average files/s is not up to 200k files/s,
so still a good 10-15% off where it should be. xfs_repair is back
down to 10-15% off where it should be, too. bulkstat still fires off
a bad page reference count warning, iscsi still panics immediately.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com

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