Upstream commit ce971233242b ("s390/cpum_cf: Deny all sampling events by counter PMU"), backported to 6.6 as commit d660c8d8142e ("s390/cpum_cf: Deny all sampling events by counter PMU"), implicitly depends on the unconditional initialization of err to -ENOENT added by upstream commit aa1ac98268cd ("s390/cpumf: Fix double free on error in cpumf_pmu_event_init()"). The latter change is missing from 6.6, resulting in an instance of -Wuninitialized, which is fairly obvious from looking at the actual diff.

arch/s390/kernel/perf_cpum_cf.c:858:10: warning: variable 'err' is uninitialized when used here [-Wuninitialized] 858 | return err; | ^~~

Commit aa1ac98268cd ("s390/cpumf: Fix double free on error in cpumf_pmu_event_init()") depends on commit c70ca298036c ("perf/core: Simplify the perf_event_alloc() error path"), which is a part of a much larger series unsuitable for stable.

Extract the unconditional initialization of err to -ENOENT from commit aa1ac98268cd ("s390/cpumf: Fix double free on error in cpumf_pmu_event_init()") and apply it to 6.6 as a standalone change to resolve the warning.

Fixes: d660c8d8142e ("s390/cpum_cf: Deny all sampling events by counter PMU") Signed-off-by: Nathan Chancellor nathan@kernel.org --- This was reported on 6.1 and the offending commit was dropped but 6.6 suffered from the same issue (I am surprised LKFT's testing caught it in the 6.1 case but not 6.6...):

https://lore.kernel.org/CADYN=9Li3gHMJ+weE0khMBmpS1Wcj-XaUeaUZg2Nxdz0qY9sdg@...

As it is already released, I figured I would just submit a fixup patch, which could also be used to fix the issue in 6.1. --- arch/s390/kernel/perf_cpum_cf.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c index 771e1cb17540..e590b4c09625 100644 --- a/arch/s390/kernel/perf_cpum_cf.c +++ b/arch/s390/kernel/perf_cpum_cf.c @@ -852,7 +852,7 @@ static int cpumf_pmu_event_type(struct perf_event *event) static int cpumf_pmu_event_init(struct perf_event *event) { unsigned int type = event->attr.type; - int err; + int err = -ENOENT;

if (is_sampling_event(event)) /* No sampling support */ return err; @@ -861,8 +861,6 @@ static int cpumf_pmu_event_init(struct perf_event *event) else if (event->pmu->type == type) /* Registered as unknown PMU */ err = __hw_perf_event_init(event, cpumf_pmu_event_type(event)); - else - return -ENOENT;

if (unlikely(err) && event->destroy) event->destroy(event);

--- base-commit: af1544b5d072514b219695b0a9fba0b1e0d5e289 change-id: 20250922-6-6-s390-cpum_cf-fix-uninit-err-010876c3d58c

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