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

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Date:   Fri, 23 Dec 2016 09:15:00 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...com>, 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 Thu, Dec 22, 2016 at 01:10:19PM -0800, Linus Torvalds wrote:
> Ok, so the numa issue was a red herring. With that fixed:
> 
> On Thu, Dec 22, 2016 at 1:06 PM, Dave Chinner <david@...morbit.com> wrote:
> >
> > 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.
> 
> Do you have CONFIG_BLK_WBT enabled, perhaps?

Ok, yes, that's enabled. Let me go turn it off and see what happens.

> It's new to this merge window, and I'm not convinced it's been tuned.
> Particularly for your kinds of fairly extreme IO loads.

Well, these aren't extreme IO workloads. Yes, the filesystem does a
lot of work on the CPU, but the IO loads XFS generates aren't
particularly high - maybe 2-3000 IOPS at most, and mostly the
bandwidth is below 100MB/s.

Cheers,

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