linux-kernel - Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE

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Date:   Wed, 23 Aug 2017 07:19:31 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Byungchul Park <byungchul.park@....com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Tejun Heo <tj@...nel.org>, Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING

On Tue, Aug 22, 2017 at 11:06:03AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 22, 2017 at 03:46:03PM +1000, Dave Chinner wrote:
> > Even if I ignore the fact that buffer completions are run on
> > different workqueues, there seems to be a bigger problem with this
> > sort of completion checking.
> > 
> > That is, the trace looks plausible because we are definitely hold an
> > inode locked deep inside a truncate operation where the completion
> > if flagged.  Indeed, some transactions that would flag like this
> > could be holding up to 5 inodes locked and have tens of other
> > metadata objects locked. There are potentially tens (maybe even
> > hundreds) of different paths into this IO wait point, and all have
> > different combinations of objects locked when it triggers. So
> > there's massive scope for potential deadlocks....
> > 
> > .... and so we must have some way of avoiding this whole class of
> > problems that lockdep is unaware of.
> 
> So I did the below little hack, which basically wipes the entire lock
> history when we start a work and thereby disregards/looses the
> dependency on the work 'lock'.

Ok, so now it treats workqueue worker threads like any other
process?

> It makes my test box able to boot and build a kernel on XFS, so while I
> see what you're saying (I think), it doesn't appear to instantly show.
> 
> Should I run xfstests or something to further verify things are OK? Does
> that need a scratch partition (I keep forgetting how to run that stuff
> :/).

A couple of 4-8GB ramdisks/fake pmem regions is all you need. Put
this in the configs/<hostname>.config file, modifying the devices
to suit:

[xfs]
FSTYP=xfs
TEST_DIR=/mnt/test
TEST_DEV=/dev/pmem0
SCRATCH_MNT=/mnt/scratch
SCRATCH_DEV=/dev/pmem1

and run "./check -s xfs -g auto" from the root of the xfstests
source tree.

Cheers,

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