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/2464313eef01c5b1edf0eccf57a32cde... [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
On Tue, 15 Jul 2025 12:56:16 -0700 Nathan Chancellor nathan@kernel.org wrote:
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().
I'll change this to "a false positive warning".
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().
--- 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); }
Ho hum OK, but the code did deteriorate a bit.
static ssize_t advisor_mode_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { const char *output;
if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) output = "none [scan-time]"; else output = "[none] scan-time";
return sysfs_emit(buf, "%s\n", output); }
Inconsistent with the other code which looks at this enum. Previously the code explicitly recognized that there are only two modes and that became implicit.
Oh well, no big deal and we don't want clang builds erroring out like this.
On 15.07.25 23:49, Andrew Morton wrote:
On Tue, 15 Jul 2025 12:56:16 -0700 Nathan Chancellor nathan@kernel.org wrote:
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().
I'll change this to "a false positive warning".
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().
--- 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); }
Ho hum OK, but the code did deteriorate a bit.
static ssize_t advisor_mode_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { const char *output;
if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) output = "none [scan-time]"; else output = "[none] scan-time";
return sysfs_emit(buf, "%s\n", output); }
Inconsistent with the other code which looks at this enum. Previously the code explicitly recognized that there are only two modes and that became implicit.
Oh well, no big deal and we don't want clang builds erroring out like this.
Acked-by: David Hildenbrand david@redhat.com
linux-stable-mirror@lists.linaro.org
-
Andrew Morton -
David Hildenbrand -
Nathan Chancellor