shmget02: reduce the shmmax test value for compat mode

As Arnd Bergmann pointed out that SHMMAX being defined as
(ULONG_MAX - (1UL << 24)), so the kernel would likely use
a large 64-bit value, while the 32-bit user space uses a
much smaller limit.

It finally results in ENOMEM failure:
  shmget02.c:95: TFAIL: shmget(1644199826, 4278190080, 1536)
                 expected EINVAL: ENOMEM (12)

With suggest by Manfred Spraul we could reduce the value
of '/proc/sys/kernel/shmmax' for compat mode and only test
the overflow behavior with default+1.

Reported-by: Linux Kernel Functional Testing <[email protected]>
Signed-off-by: Li Wang <[email protected]>
Cc: Naresh Kamboju <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Manfred Spraul <[email protected]>
Reviewed-by: Martin Doucha <[email protected]>

Author: wangli5665

testcases/kernel/syscalls/ipc/shmget/shmget02.c

@@ -56,7 +56,7 @@ static struct tcase {
 	{&shmkey1, SHM_SIZE, IPC_EXCL, 0, 0, ENOENT},
 	{&shmkey, SHM_SIZE, IPC_CREAT | IPC_EXCL, 0, 0, EEXIST},
 	{&shmkey1, SHMMIN - 1, IPC_CREAT | IPC_EXCL, 0, 0, EINVAL},
-	{&shmkey1, SHMMAX + 1, IPC_CREAT | IPC_EXCL, 0, 0, EINVAL},
+	{&shmkey1, 8192 + 1, IPC_CREAT | IPC_EXCL, 0, 0, EINVAL},
 	{&shmkey, SHM_SIZE * 2, IPC_EXCL, 0, 0, EINVAL},
 	{&shmkey, SHM_SIZE, SHM_RD, 1, 0, EACCES},
 	{&shmkey1, SHM_SIZE, IPC_CREAT | SHM_HUGETLB, 0, 1, EPERM},
@@ -149,4 +149,8 @@ static struct tst_test test = {
 	.test = do_test,
 	.tcnt = ARRAY_SIZE(tcases),
 	.hugepages = {TST_NO_HUGEPAGES},
+	.save_restore = (const struct tst_path_val[]) {
+		{"/proc/sys/kernel/shmmax", "8192", TST_SR_TCONF_MISSING | TST_SR_TBROK_RO},
+		{}
+	},
 };