Re: btrfs bio linked list corruption.

[Chris Mason]

On 10/13/2016 02:16 PM, Dave Jones wrote:
> On Wed, Oct 12, 2016 at 10:42:46AM -0400, Chris Mason wrote:
>  > On 10/12/2016 10:40 AM, Dave Jones wrote:
>  > > On Wed, Oct 12, 2016 at 09:47:17AM -0400, Dave Jones wrote:
>  > >  > On Tue, Oct 11, 2016 at 11:54:09AM -0400, Chris Mason wrote:
>  > >  >  >
>  > >  >  >
>  > >  >  > On 10/11/2016 10:45 AM, Dave Jones wrote:
>  > >  >  > > This is from Linus' current tree, with Al's iovec fixups on top.
>  > >  >  > >
>  > >  >  > > ------------[ cut here ]------------
>  > >  >  > > WARNING: CPU: 1 PID: 3673 at lib/list_debug.c:33 __list_add+0x89/0xb0
>  > >  >  > > list_add corruption. prev->next should be next (ffffe8ffff806648), but was ffffc9000067fcd8. (prev=ffff880503878b80).
>  > >  >  > > CPU: 1 PID: 3673 Comm: trinity-c0 Not tainted 4.8.0-think+ #13
>  > >  >  > >  ffffc90000d87458 ffffffff8d32007c ffffc90000d874a8 0000000000000000
>  > >  >  > >  ffffc90000d87498 ffffffff8d07a6c1 0000002100000246 ffff88050388e880
>  > >  >
>  > >  > I hit this again overnight, it's the same trace, the only difference
>  > >  > being slightly different addresses in the list pointers:
>  > >  >
>  > >  > [42572.777196] list_add corruption. prev->next should be next (ffffe8ffff806648), but was ffffc90000647cd8. (prev=ffff880503a0ba00).
>  > >  >
>  > >  > I'm actually a little surprised that ->next was the same across two
>  > >  > reboots on two different kernel builds.  That might be a sign this is
>  > >  > more repeatable than I'd thought, even if it does take hours of runtime
>  > >  > right now to trigger it.  I'll try and narrow the scope of what trinity
>  > >  > is doing to see if I can make it happen faster.
>  > >
>  > > .. and of course the first thing that happens is a completely different
>  > > btrfs trace..
>  > >
>  > >
>  > > WARNING: CPU: 1 PID: 21706 at fs/btrfs/transaction.c:489 start_transaction+0x40a/0x440 [btrfs]
>  > > CPU: 1 PID: 21706 Comm: trinity-c16 Not tainted 4.8.0-think+ #14
>  > >  ffffc900019076a8 ffffffffb731ff3c 0000000000000000 0000000000000000
>  > >  ffffc900019076e8 ffffffffb707a6c1 000001e9f5806ce0 ffff8804f74c4d98
>  > >  0000000000000801 ffff880501cfa2a8 000000000000008a 000000000000008a
>  >
>  > This isn't even IO.  Uuughhhh.  We're going to need a fast enough test
>  > that we can bisect.
>
> Progress...
> I've found that this combination of syscalls..
>
> ./trinity -C64 -q -l off -a64 --enable-fds=testfile -c fsync -c fsetxattr -c lremovexattr -c pwritev2
>
> hits one of these two bugs in a few minutes runtime.
>
> Just the xattr syscalls + fsync isn't enough, neither is just pwrite + fsync.
> Mix them together though, and something goes awry.

Hasn't triggered here yet.  I'll leave it running though.

-chris