Re: Rambling noise #1: generic/230 can trigger kernel debug lock detector

[Dave Chinner <david@fromorbit.com>]

On Thu, May 09, 2013 at 10:00:10PM -0400, Michael L. Semon wrote:
> On 05/09/2013 03:20 AM, Dave Chinner wrote:
> >On Thu, May 09, 2013 at 01:16:46PM +1000, Dave Chinner wrote:
> >>On Wed, May 08, 2013 at 10:24:25PM -0400, Michael L. Semon wrote:
> >>>Hi!  I'm trying to come up with a series of ramblings that may or
> >>>may not be useful in a mailing-list context, with the idea that one
> >>>bug report might be good, the next might be me thinking aloud with
> >>>data in hand because I know something's wrong but can't put my
> >>>finger on it.  An ex-girlfriend saw the movie "Rain Man" years ago
> >>>pointed to the screen and said, "Do you see that guy?  That's you!"
> >>>If only I could be so smart...or act as well as Dustin Hoffman.  The
> >>>noisy thinking is there, just not the brilliant insights...
> >>>
> >>>This report is to pass on a kernel lock detector message that might
> >>>be reproducible under a certain family of tests.  generic/230 may
> >>>not be at fault, it's just where the detector went off.
> >>
> >>No, there's definitely a bug there. Thanks for the report, Michael.
> >>Try the patch below.
> >
> >Actaully, there's a bug in the error handling in that version - it
> >fails to unlock the quotaoff lock properly on failure. The version
> >below fixes that problem.
> >
> >Cheers,
> >
> >Dave.
> 
> OK, I'll try this version as well.  The first version seemed to work
> just fine.

It should, the bug was in an error handling path you are unlikely to
hit.

> xfs/012 13s ...[ 1851.323902]
> [ 1851.325479] =================================
> [ 1851.326551] [ INFO: inconsistent lock state ]
> [ 1851.326551] 3.9.0+ #1 Not tainted
> [ 1851.326551] ---------------------------------
> [ 1851.326551] inconsistent {RECLAIM_FS-ON-R} -> {IN-RECLAIM_FS-W} usage.
> [ 1851.326551] kswapd0/18 [HC0[0]:SC0[0]:HE1:SE1] takes:
> [ 1851.326551]  (&(&ip->i_lock)->mr_lock){++++-+}, at: [<c11dcabf>]
> xfs_ilock+0x10f/0x190
> [ 1851.326551] {RECLAIM_FS-ON-R} state was registered at:
> [ 1851.326551]   [<c105e10a>] mark_held_locks+0x8a/0xf0
> [ 1851.326551]   [<c105e69c>] lockdep_trace_alloc+0x5c/0xa0
> [ 1851.326551]   [<c109c52c>] __alloc_pages_nodemask+0x7c/0x670
> [ 1851.326551]   [<c10bfd8e>] new_slab+0x6e/0x2a0
> [ 1851.326551]   [<c14083a9>] __slab_alloc.isra.59.constprop.67+0x1d3/0x40a
> [ 1851.326551]   [<c10c12cd>] __kmalloc+0x10d/0x180
> [ 1851.326551]   [<c1199b56>] kmem_alloc+0x56/0xd0
> [ 1851.326551]   [<c1199be1>] kmem_zalloc+0x11/0xd0
> [ 1851.326551]   [<c11c666e>] xfs_dabuf_map.isra.2.constprop.5+0x22e/0x520

Yup, needs a KM_NOFS allocation there because we come through
here outside a transaction and so it doesn't get KM_NOFS implicitly
in this case. There's been a couple of these reported in the past
week or two - I need to do an audit and sweep them all up....

Technically, though, this can't cause a deadlock on the inode we
hold a lock on here because it's a directory inode, not a regular
file and so it will never be seen in the reclaim data writeback path
nor on the inode LRU when the shrinker runs. So most likely it is a
false positive...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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