mm-pgtable-reclaim-empty-pte-page-in-madvisemadv_dontneed-fix

Dan Carpenter reported the following warning:

Commit e3aafd2d35 ("mm: pgtable: reclaim empty PTE page in
madvise(MADV_DONTNEED)") from Dec 4, 2024 (linux-next), leads to the
following Smatch static checker warning:

	mm/pt_reclaim.c:69 try_to_free_pte()
	error: uninitialized symbol 'ptl'.

To fix it, assign an initial value of NULL to the ptl.

Link: https://lkml.kernel.org/r/20241206112348.51570-1-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-mm/224e6a4e-43b5-4080-bdd8-b0a6fb2f0853@stanley.mountain/
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/pt_reclaim.c

@@ -36,7 +36,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr,
 		     struct mmu_gather *tlb)
 {
 	pmd_t pmdval;
-	spinlock_t *pml, *ptl;
+	spinlock_t *pml, *ptl = NULL;
 	pte_t *start_pte, *pte;
 	int i;