[PATCH] another kmap imbalance in 2.4.x/2.5.x RPC

  We've uncovered yet another kmap imbalance in the new RPC code.  This
looks like it might be the last one (my debugging printks have been
unable to unearth any more).  One line fix + 4 line comment appended.

net/sunrpc/xdr.c

@@ -244,6 +244,11 @@ void xdr_kunmap(struct xdr_buf *xdr, size_t base)
 		pglen -= base;
 		base  += xdr->page_base;
 		ppage += base >> PAGE_CACHE_SHIFT;
+		/* Note: The offset means that the length of the first
+		 * page is really (PAGE_CACHE_SIZE - (base & ~PAGE_CACHE_MASK)).
+		 * In order to avoid an extra test inside the loop,
+		 * we bump pglen here, and just subtract PAGE_CACHE_SIZE... */
+		pglen += base & ~PAGE_CACHE_MASK;
 	}
 	for (;;) {
 		flush_dcache_page(*ppage);