linux-kernel - [PATCH 5.13 279/300] x86/resctrl: Fix a maybe-uninitialized build warning treated as error

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Date:   Mon, 13 Sep 2021 15:15:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Terry Bowman <Terry.Bowman@....com>,
        kernel test robot <lkp@...el.com>,
        Babu Moger <babu.moger@....com>, Borislav Petkov <bp@...e.de>,
        Reinette Chatre <reinette.chatre@...el.com>
Subject: [PATCH 5.13 279/300] x86/resctrl: Fix a maybe-uninitialized build warning treated as error

From: Babu Moger <babu.moger@....com>

commit 527f721478bce3f49b513a733bacd19d6f34b08c upstream.

The recent commit

  064855a69003 ("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: 064855a69003 ("x86/resctrl: Fix default monitoring groups reporting")
Reported-by: Terry Bowman <Terry.Bowman@....com>
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Babu Moger <babu.moger@....com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/162949631908.23903.17090272726012848523.stgit@bmoger-ubuntu
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/cpu/resctrl/monitor.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -304,6 +304,12 @@ static u64 __mon_event_count(u32 rmid, s
 	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) {