Hi!

It's a freshly downloaded linux-2.5.4.tar.bz2. The usual make oldconfig 
dep clean bzImage:

scripts/split-include include/linux/autoconf.h include/config
gcc -D__KERNEL__ -I/home/zozo/kernel-dev/linux-2.5.4/include -Wall 
-Wstrict-prototypes -Wno-trigraphs -O2 -fomit-frame-pointer 
-fno-strict-aliasing -fno-common -pipe -mpreferred-stack-boundary=2 
-march=i686   -DKBUILD_BASENAME=main -c -o init/main.o init/main.c
In file included from 
/home/zozo/kernel-dev/linux-2.5.4/include/asm/thread_info.h:13,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/thread_info.h:10,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/spinlock.h:7,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/mmzone.h:8,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/gfp.h:4,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/slab.h:14,
                 from 
/home/zozo/kernel-dev/linux-2.5.4/include/linux/proc_fs.h:5,
                 from init/main.c:15:
/home/zozo/kernel-dev/linux-2.5.4/include/asm/processor.h: In function 
`thread_saved_pc':
/home/zozo/kernel-dev/linux-2.5.4/include/asm/processor.h:444: 
dereferencing pointer to incomplete type
/home/zozo/kernel-dev/linux-2.5.4/include/asm/processor.h:445: warning: 
control reaches end of non-void function
make: *** [init/main.o] Error 1

It looks like <asm/processor.h> needs to #include <linux/sched.h> somewhere
as drawn is "schedh-after.ps.gz". Config is attached.

<nothumorous>
The compilation certainly finishes sooner after the "sched.h cleanup".  ;-)
</nothumorous>

Best regards,
Zoltán Böszörményi