linux-kernel - Re: Linux 3.0 release - btrfs possible locking deadlock

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Message-Id: <201107252022.03834.edt@aei.ca>
Date:	Mon, 25 Jul 2011 20:22:03 -0400
From:	Ed Tomlinson <edt@....ca>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-btrfs" <linux-btrfs@...r.kernel.org>,
	Josef Bacik <josef@...hat.com>
Subject: Re: Linux 3.0 release - btrfs possible locking deadlock

On Monday 25 July 2011 15:49:37 Chris Mason wrote:
> Excerpts from Ed Tomlinson's message of 2011-07-22 19:21:00 -0400:
> > On Thursday 21 July 2011 22:59:53 Linus Torvalds wrote:
> > > So there it is. Gone are the 2.6.<bignum> days, and 3.0 is out.
> > > 
> > 
> > Hi,
> > 
> > Managed to get this with btrfs rsync(ing) from ext4 to a btrfs fs with three partitions using raid1.
> > 
> > [16018.211493] device fsid f7186eeb-60df-4b1a-890a-4a1eb42f81fe devid 1 transid 10 /dev/sdd4
> > [16018.230643] btrfs: use lzo compression
> > [16018.234619] btrfs: enabling disk space caching
> > [25949.414011] 
> > [25949.414011] =======================================================
> > [25949.416549] [ INFO: possible circular locking dependency detected ]
> > [25949.423187] 3.0.0-crc+ #348
> > [25949.423187] -------------------------------------------------------
> > [25949.423187] rsync/20237 is trying to acquire lock:
> > [25949.423187]  (btrfs-extent-01){+.+...}, at: [<ffffffffa047ce88>] btrfs_try_spin_lock+0x78/0xb0 [btrfs]
> > [25949.423187] 
> > [25949.423187] but task is already holding lock:
> > [25949.423187]  (&(&eb->lock)->rlock){+.+...}, at: [<ffffffffa047cee2>] btrfs_clear_lock_blocking+0x22/0x30 [btrfs]
> > [25949.423187] 
> > [25949.423187] which lock already depends on the new lock.
> > 
> > Kernel is 3.0.0 without any extras.
> > 
> > Ideas?
> 
> Did this actually deadlock?  lockdep has issues with the btrfs
> clear_lock_blocking code, and I need to redo the annotations a bit.  The
> problem is that we have the same lock class representing unrelated locks from
> different trees.

It did not stop any processes that I could see and the rsync did complete ok.  Thats why I said possible.
Figured it might be something you needed to see and/or fix though.

Thanks
Ed
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