[2.6.23] tasks stuck in running state?

[Jeff Garzik <jeff@garzik.org>]

On my main devel box, vanilla 2.6.23 on x86-64/Fedora-7, I'm seeing a 
certain behavior at least once a day.  I'll start a kernel build (make 
-sj5 on this box), and it will "hang" in the following way:

> 31003 ?        S      0:04 sshd: jgarzik@pts/0
> 31004 pts/0    Ss     0:02  \_ -bash
>  8280 pts/0    S+     0:00      \_ make ARCH=i386 -sj4
>  8690 pts/0    Z+     0:00          \_ [rm] <defunct>
>  8691 pts/0    S+     0:00          \_ /bin/sh -c cat include/config/kernel.release 2> /dev/null
>  8692 pts/0    R+     6:12              \_ cat include/config/kernel.release

Specifically, the symptom is a process, often a simple one like cat(1) 
or rm(1) or somewhere in check-headers, will stay in the running state, 
accumulating CPU time.

If I Ctrl-C the build, and start over, the build will normally -not- get 
stuck at the same point, but proceed to chew through one of a bazillion 
allmodconfig builds.

I also see this occasionally on my main workstation (also 
2.6.23/x86-64/Fedora-7), though not as frequently.

This is a new behavior since the new scheduler was merged... I think.

Nothing more concrete to report at this time.  I cannot easily reproduce 
the behavior, as it happens [apparently] randomly sometime during the 
day.  Generally, the files these programs are dealing with are -always- 
in the pagecache, if that makes any difference.

	Jeff