[PATCH] mm/ksm: Fix -Wsometimes-uninitialized from clang-21 in advisor_mode_show()

[Nathan Chancellor <nathan@kernel.org>]

After a recent change in clang to expose uninitialized warnings from
const variables [1], there is a warning from the if statement in
advisor_mode_show().

  mm/ksm.c:3687:11: error: variable 'output' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
   3687 |         else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
        |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  mm/ksm.c:3690:33: note: uninitialized use occurs here
   3690 |         return sysfs_emit(buf, "%s\n", output);
        |                                        ^~~~~~

Rewrite the if statement to implicitly make KSM_ADVISOR_NONE the else
branch so that it is obvious to the compiler that ksm_advisor can only
be KSM_ADVISOR_NONE or KSM_ADVISOR_SCAN_TIME due to the assignments in
advisor_mode_store().

Cc: stable@vger.kernel.org
Fixes: 66790e9a735b ("mm/ksm: add sysfs knobs for advisor")
Closes: https://github.com/ClangBuiltLinux/linux/issues/2100
Link: https://github.com/llvm/llvm-project/commit/2464313eef01c5b1edf0eccf57a32cdee01472c7 [1]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 mm/ksm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 2b0210d41c55..160787bb121c 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3682,10 +3682,10 @@ static ssize_t advisor_mode_show(struct kobject *kobj,
 {
 	const char *output;
 
-	if (ksm_advisor == KSM_ADVISOR_NONE)
-		output = "[none] scan-time";
-	else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
+	if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
 		output = "none [scan-time]";
+	else
+		output = "[none] scan-time";
 
 	return sysfs_emit(buf, "%s\n", output);
 }

---
base-commit: fed48693bdfeca666f7536ba88a05e9a4e5523b6
change-id: 20250715-ksm-fix-clang-21-uninit-warning-bea5a6b886ce

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>