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Date:      Fri, 15 Jun 2007 14:25:21 -0400
From:      Kris Kennaway <kris@obsecurity.org>
To:        Benjamin Close <Benjamin.Close@clearchain.com>
Cc:        freebsd-current@freebsd.org
Subject:   Re: Swapfile on ZFS & Deadlock
Message-ID:  <20070615182521.GB9619@rot13.obsecurity.org>
In-Reply-To: <4672945C.3060304@clearchain.com>
References:  <4672945C.3060304@clearchain.com>

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On Fri, Jun 15, 2007 at 11:00:04PM +0930, Benjamin Close wrote:
> Hi All,
>    Whilst running out of memory compiling Xorg (scanPCI is a killer) I=20
> discovered a quick way to deadlock the system:
>=20
> dd if=3D/dev/zero of=3Dsomefileonzfs bs=3Dsomething count=3Dsomething
> mdconfig -a -f something
> swapon /dev/md0
>=20
> Then do something that needs swap.. instant deadlock. The system is=20
> still responsive but all disk access become hung.
>=20
> Known issue? If so is there a way we can warn users/prevent users from=20
> doing it?

Enable DEBUG_VFS_LOCKS and DEBUG_LOCKS, then break to DDB when the
deadlock occurs and do 'show lockedvnods'.

Kris

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