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XFS in a XFS locks up in xfs_ilock

To: xfs@xxxxxxxxxxx
Subject: XFS in a XFS locks up in xfs_ilock
From: Jan Engelhardt <jengelh@xxxxxxxxxx>
Date: Fri, 23 Oct 2009 20:02:08 +0200 (CEST)
User-agent: Alpine 2.00 (LSU 1167 2008-08-23)

it seems that somewhere, locking is afoul in XFS so that having a 
loopback XFS on an XFS causes a deadlock, first on the subvolume, then 
on the real one. Sometimes that happens within writing a few MB to the 
subvolume (the loop one), sometimes nothing happens and it can be used 
for many months.

Suggested testcase:

Starting out with $HOME being on xfs (truncate is coreutils 7+):
$ >disk
$ truncate --size=$[3*1048576*1024] disk
So it's actually sparse(!)
$ mkfs.xfs disk
# mount disk mnt -oloop

Start filling it with data, preferably something like installing a bunch 
of rpm/debs into mnt, and hopefully soon enough, the thing will lock up.
xfs_ilock I got from `ps xaf -o wchan` while a box was shortly before 
dying - processes were stuck in D state. Not sure if this is related to 
the sparseness of the file, but I would bet it's part of the problem.

This has been observed on 2.6.29-, probably even earlier.


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