2.6.39, 3.0.0-rc7+: complete system freeze with rsync on big directory

[Michael Brade <brade@informatik.uni-muenchen.de>]

Hi,

this is perfectly reproducible: with vanilla 2.6.39.x and 3.0.0 from 
yesterday's git my system completely freezes after a minute or so when I do

   rsync -cavSH -n /source/ /dest/

Watching htop, it freezes only after the caches are full but not immediately 
when the caches are full. No Alt-SysRq-magic is working anymore, nothing 
responds at all after the freeze. This is on tty1, no X server running.

Note the -n which means dry run. I also mounted both directories read-only, so 
it's not the write commands. I am using XFS on both directories, one is 
mounted with iscsi, the other is local and encrypted with loop-aes. The 
directory size is >20 GB, 4000-6000 files. I first noticed it when a 
cp -a /source /dest froze the system.

When I go back to 2.6.37.6 it works fine. I didn't try 2.6.38 yet.

I am running this on a Dell Vostro, amd64, 6 GB RAM, 8x Intel Core i7 CPU Q 
740 @ 1.73GHz.

Any ideas how to debug this despite the freeze? Do you need my kernel config? 
Do you need any other info? Please CC me.

thanks,
   Michael