2.6.38 comes with a bunch of new dentry flags and one of them conflicts with our DCACHE_LUSTRE_INVALID:

From lustre/llite/llite_internal.h:

#ifndef DCACHE_LUSTRE_INVALID
#define DCACHE_LUSTRE_INVALID 0x4000
#endif

From include/linux/dcache.h:

#define DCACHE_OP_HASH 0x1000
#define DCACHE_OP_COMPARE 0x2000
#define DCACHE_OP_REVALIDATE 0x4000
#define DCACHE_OP_DELETE 0x8000

Those flags were introduced by the following commit:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=fb045adb99d9b7c562dc7fef834857f78249daa1

I'm not sure when we will jump to 2.6.38, but this is definitely something to keep in mind ...