Build problem in sched.c in 2.5.23

[Joseph Pingenot]

make[1]: Entering directory `/usr/local/src/kernel/linux-2.5.23/kernel'
  gcc -Wp,-MD,./.sched.o.d -D__KERNEL__ -I/usr/local/src/kernel/linux-2.5.23/include -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fomit-frame-pointer -fno-strict-aliasing -fno-common -pipe -mpreferred-stack-boundary=2 -march=i686 -nostdinc -iwithprefix include    -fno-omit-frame-pointer -DKBUILD_BASENAME=sched   -c -o sched.o sched.c
sched.c: In function `sys_sched_setaffinity':
sched.c:1332: `cpu_online_map' undeclared (first use in this function)
sched.c:1332: (Each undeclared identifier is reported only once
sched.c:1332: for each function it appears in.)
sched.c: In function `sys_sched_getaffinity':
sched.c:1391: `cpu_online_map' undeclared (first use in this function)
make[1]: *** [sched.o] Error 1
make[1]: Leaving directory `/usr/local/src/kernel/linux-2.5.23/kernel'
make: *** [kernel] Error 2

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