x86/resctrl: Fix a maybe-uninitialized build warning treated as error

stable inclusion
from stable-5.10.65
commit c6b42ec1c93655f00f4438ed32acb8c84ff127f2
bugzilla: 182361 https://gitee.com/openeuler/kernel/issues/I4EH3U

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6b42ec1c93655f00f4438ed32acb8c84ff127f2

--------------------------------

commit 527f7214 upstream.

The recent commit

  064855a6 ("x86/resctrl: Fix default monitoring groups reporting")

caused a RHEL build failure with an uninitialized variable warning
treated as an error because it removed the default case snippet.

The RHEL Makefile uses '-Werror=maybe-uninitialized' to force possibly
uninitialized variable warnings to be treated as errors. This is also
reported by smatch via the 0day robot.

The error from the RHEL build is:

  arch/x86/kernel/cpu/resctrl/monitor.c: In function ‘__mon_event_count’:
  arch/x86/kernel/cpu/resctrl/monitor.c:261:12: error: ‘m’ may be used
  uninitialized in this function [-Werror=maybe-uninitialized]
    m->chunks += chunks;
              ^~

The upstream Makefile does not build using '-Werror=maybe-uninitialized'.
So, the problem is not seen there. Fix the problem by putting back the
default case snippet.

 [ bp: note that there's nothing wrong with the code and other compilers
   do not trigger this warning - this is being done just so the RHEL compiler
   is happy. ]

Fixes: 064855a6 ("x86/resctrl: Fix default monitoring groups reporting")
Reported-by: NTerry Bowman <Terry.Bowman@amd.com>
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NBabu Moger <babu.moger@amd.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Reviewed-by: NReinette Chatre <reinette.chatre@intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/162949631908.23903.17090272726012848523.stgit@bmoger-ubuntuSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/x86/kernel/cpu/resctrl/monitor.c

@@ -241,6 +241,12 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
 		m = &rr->d->mbm_local[rmid];
 		break;
+	default:
+		/*
+		 * Code would never reach here because an invalid
+		 * event id would fail the __rmid_read.
+		 */
+		return RMID_VAL_ERROR;
 	}
 
 	if (rr->first) {