Swapfile on ZFS & Deadlock

[Kris Kennaway]

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 
> discovered a quick way to deadlock the system:
> 
> dd if=/dev/zero of=somefileonzfs bs=something count=something
> mdconfig -a -f something
> swapon /dev/md0
> 
> Then do something that needs swap.. instant deadlock. The system is 
> still responsive but all disk access become hung.
> 
> Known issue? If so is there a way we can warn users/prevent users from 
> 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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