linux-kernel - Re: [git pull] vfs pile 1 (splice)

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Message-ID: <CA+55aFxFuQxaS4iMsu2x3BC5qWFfDtdSGWmsMQSFt-bAsyZJVg@mail.gmail.com>
Date:   Sun, 9 Oct 2016 12:11:58 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...com>, "Ted Ts'o" <tytso@....edu>,
        Christoph Lameter <cl@...ux.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [git pull] vfs pile 1 (splice)

On Sun, Oct 9, 2016 at 11:40 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'll continue with *just* SLUB debugging on, but I thought it was
> interesting how enabling more memory access debugging actually ends up
> changing some really subtle code.

Indeed, now with DEBUG_PAGEALLOC disabled, I got a crash again. It
apparently happened earlier in the call chain (so maybe the slub
debugging found something), which should be good. Except it now
happens in a context where I just see a hung machine, and nothing
makes it onto the screen or into the logs ;(

So this thing is apparently not all that hard to trigger, but it
doesn't exactly seem easy either. It tends to happen fairly soon after
a reboot, which makes me suspect it's some cold-cache issue, but that
doesn't narrow things down as much as you'd think. It could still be
the block layer changes, but it could also equally well be the ext4
changes.

I don't think there's any splice activity anywhere, but who knows. And
the splice changes could have buggered the pipe locking, so..

Anyway, I don't think I can bisect it, but I'll try to narrow it down
a *bit* at least.

Not doing any more pulls on this unstable base, I've been puttering
around in trying to clean up some stupid printk logging issues
instead.

                  Linus