From owner-freebsd-current@FreeBSD.ORG  Fri Jun 15 13:30:30 2007
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From: Benjamin Close <Benjamin.Close@clearchain.com>
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Subject: Swapfile on ZFS & Deadlock
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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?

Cheers,
    Benjamin