linux-kernel - Re: bio linked list corruption.

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Date:   Fri, 21 Oct 2016 16:17:48 -0400
From:   Chris Mason <clm@...com>
To:     Dave Jones <davej@...emonkey.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...com>, Al Viro <viro@...iv.linux.org.uk>,
        Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: bio linked list corruption.



On 10/21/2016 04:02 PM, Dave Jones wrote:
> On Thu, Oct 20, 2016 at 04:23:32PM -0700, Andy Lutomirski wrote:
>  > On Thu, Oct 20, 2016 at 4:03 PM, Dave Jones <davej@...emonkey.org.uk> wrote:
>  > > On Thu, Oct 20, 2016 at 04:01:12PM -0700, Andy Lutomirski wrote:
>  > >  > On Thu, Oct 20, 2016 at 3:50 PM, Dave Jones <davej@...emonkey.org.uk> wrote:
>  > >  > > On Tue, Oct 18, 2016 at 06:05:57PM -0700, Andy Lutomirski wrote:
>  > >  > >
>  > >  > >  > One possible debugging approach would be to change:
>  > >  > >  >
>  > >  > >  > #define NR_CACHED_STACKS 2
>  > >  > >  >
>  > >  > >  > to
>  > >  > >  >
>  > >  > >  > #define NR_CACHED_STACKS 0
>  > >  > >  >
>  > >  > >  > in kernel/fork.c and to set CONFIG_DEBUG_PAGEALLOC=y.  The latter will
>  > >  > >  > force an immediate TLB flush after vfree.
>  > >  > >
>  > >  > > I can give that idea some runtime, but it sounds like this a case where
>  > >  > > we're trying to prove a negative, and that'll just run and run ? In which case I
>  > >  > > might do this when I'm travelling on Sunday.
>  > >  >
>  > >  > The idea is that the stack will be free and unmapped immediately upon
>  > >  > process exit if configured like this so that bogus stack accesses (by
>  > >  > the CPU, not DMA) would OOPS immediately.
>  > >
>  > > oh, misparsed. ok, I can definitely get behind that idea then.
>  > > I'll do that next.
>  > >
>  >
>  > It could be worth trying this, too:
>  >
>  > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/vmap_stack&id=174531fef4e8
>  >
>  > It occurred to me that the current code is a little bit fragile.
>
> It's been nearly 24hrs with the above changes, and it's been pretty much
> silent the whole time.
>
> The only thing of note over that time period has been a btrfs lockdep
> warning that's been around for a while, and occasional btrfs checksum
> failures, which I've been seeing for a while, but seem to have gotten
> worse since 4.8.

Meaning you hit them with v4.8 or not?

>
> I'm pretty confident in the disk being ok in this machine, so I think
> the checksum warnings are bogus.  Chris suggested they may be the result
> of memory corruption, but there's little else going on.
>
>
> BTRFS warning (device sda3): csum failed ino 130654 off 0 csum 2566472073 expected csum 3008371513
> BTRFS warning (device sda3): csum failed ino 131057 off 4096 csum 3563910319 expected csum 738595262
> BTRFS warning (device sda3): csum failed ino 131176 off 4096 csum 1344477721 expected csum 441864825
> BTRFS warning (device sda3): csum failed ino 131241 off 245760 csum 3576232181 expected csum 2566472073
> BTRFS warning (device sda3): csum failed ino 131429 off 0 csum 1494450239 expected csum 2646577722
> BTRFS warning (device sda3): csum failed ino 131471 off 0 csum 3949539320 expected csum 3828807800
> BTRFS warning (device sda3): csum failed ino 131471 off 4096 csum 3475108475 expected csum 2566472073
> BTRFS warning (device sda3): csum failed ino 131471 off 958464 csum 142982740 expected csum 2566472073
> BTRFS warning (device sda3): csum failed ino 131471 off 0 csum 3949539320 expected csum 3828807800
> BTRFS warning (device sda3): csum failed ino 131532 off 270336 csum 3138898528 expected csum 2566472073
> BTRFS warning (device sda3): csum failed ino 131532 off 1249280 csum 2169165042 expected csum 2566472073
> BTRFS warning (device sda3): csum failed ino 131649 off 16384 csum 2914965650 expected csum 1425742005
>
>
> A curious thing: the expected csum 2566472073 turns up a number of times for different inodes, and gets
> differing actual csums each time.  I suppose this could be something like a block of all zeros in multiple files,
> but it struck me as surprising.
>
> btrfs people: is there an easy way to map those inodes to a filename ? I'm betting those are the
> test files that trinity generates. If so, it might point to a race somewhere.

btrfs inspect inode 130654 mntpoint

-chris