selftest/mremap_test: avoid crash with static build

With a large mmap map size, we can overlap with the text area and using
MAP_FIXED results in unmapping that area. Switch to MAP_FIXED_NOREPLACE
and handle the EEXIST error.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Reviewed-by: Kalesh Singh <[e-mail]>
Cc: Christophe Leroy <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Joel Fernandes <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/vm/mremap_test.c

···
 retry:
 	addr += c.src_alignment;
 	src_addr = mmap((void *) addr, c.region_size, PROT_READ | PROT_WRITE,
-			MAP_FIXED | MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+			MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
+			-1, 0);
 	if (src_addr == MAP_FAILED) {
-		if (errno == EPERM)
+		if (errno == EPERM || errno == EEXIST)
 			goto retry;
 		goto error;
 	}