Re: [akpm-mm:mm-new] BUILD SUCCESS WITH UNVERIFIED WARNING e0ffd277b09a7c9f1a436e5f75be37ac490bc59f

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 Aug 2026 10:44:13 +0800 kernel test robot <lkp@intel.com> wrote:

> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-new
> branch HEAD: e0ffd277b09a7c9f1a436e5f75be37ac490bc59f  mm/swap, PM: hibernate: atomically replace hibernation pin
> 
> Unverified Warning (likely false positive, kindly check if interested):
> 
>     https://lore.kernel.org/oe-kbuild/202607120402.clBrrZQA-lkp@intel.com
> 
>     mm/hmm.c:673 hmm_do_fault() error: we previously assumed 'hmm_vma_walk->locked' could be null (see line 654)
> 
> Warning ids grouped by kconfigs:

Thanks.  I assume this warning was produced by sparse?  The report
doesn't tell us this, and I suggest that it do so.

> recent_errors
> `-- s390-randconfig-r071-20260809
>     `-- mm-hmm.c-hmm_do_fault()-error:we-previously-assumed-hmm_vma_walk-locked-could-be-null-(see-line-)

Caused by

	121170831228 ("mm/hmm: add hmm_range_fault_unlocked_timeout() for mmap lock-drop support")


Stanislaw, you've previously said that this is a can't-happen, but boy
I'm getting tired of seeing this warning report.  Would the below change
hurt anything?  I can't immediately think of a cost-free way of doing
this.


From: Andrew Morton <akpm@linux-foundation.org>
Subject: mm/hmm.c:hmm_do_fault(): suppress sparse warning
Date: Mon Aug 10 01:16:37 PM PDT 2026

mm/hmm.c:673 hmm_do_fault() error: we previously assumed 'hmm_vma_walk->locked' could be null (see line 654)

Stanislav says this can't happen.  Waste a few cycles to make the warning
go away.

Fixes: 121170831228 ("mm/hmm: add hmm_range_fault_unlocked_timeout() for mmap lock-drop support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/202608101053.PhnVUM4u-lkp@intel.com
Cc: Stanislav Kinsburskii <skinsburskii@gmail.com>
Cc: David Hildenbrand <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hmm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/hmm.c~mm-hmmc-hmm_do_fault-suppress-sparse-warning
+++ a/mm/hmm.c
@@ -670,7 +670,8 @@ static int hmm_do_fault(struct mm_struct
 		ret = handle_mm_fault(vma, addr, fault_flags, NULL);
 
 		if (ret & (VM_FAULT_COMPLETED | VM_FAULT_RETRY)) {
-			*hmm_vma_walk->locked = false;
+			if (hmm_vma_walk->locked)	/* needed by sparse */
+				*hmm_vma_walk->locked = false;
 			return HMM_FAULT_UNLOCKED;
 		}
 
_