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Thu, 02 Apr 2026 19:56:20 -0700 (PDT) From: Qing Wang To: urezki@gmail.com Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+37b7f6cd519f7fb8d32a@syzkaller.appspotmail.com, wangqing7171@gmail.com Subject: Re: [PATCH] mm/vmalloc: fix KMSAN uninit-value warning in decay_va_pool_node() Date: Fri, 3 Apr 2026 10:56:14 +0800 Message-Id: <20260403025614.2032877-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Thu, 02 Apr 2026 at 23:45, Uladzislau Rezki wrote: > > KMSAN reported an uninit-value warning when accessing vmap_area->list > > in decay_va_pool_node(): > > > > BUG: KMSAN: uninit-value in __list_del_entry_valid include/linux/list.h:-1 [inline] > > BUG: KMSAN: uninit-value in __list_del_entry include/linux/list.h:223 [inline] > > BUG: KMSAN: uninit-value in list_del_init include/linux/list.h:295 [inline] > > BUG: KMSAN: uninit-value in decay_va_pool_node+0xf78/0x1dd0 mm/vmalloc.c:2255 > > > > Uninit was created at: > > kmem_cache_alloc_node_noprof+0x3cd/0x12d0 mm/slub.c:4918 > > alloc_vmap_area+0x327/0x2e30 mm/vmalloc.c:2065 > > > > The root cause is that if node_alloc() fail and the va is allocated via > > kmem_cache_alloc_node() by alloc_vmap_area(), va->list will be uninitialized. > > > > Fix this by explicitly initializing va->list after allocation. > > > > Reported-by: syzbot+37b7f6cd519f7fb8d32a@syzkaller.appspotmail.com > > Closes: https://syzkaller.appspot.com/bug?extid=37b7f6cd519f7fb8d32a > > > I can not access two above links. Are they valid? I would like to have > a look at report. I recheck the 'Closes' link and it's valid. > > > Signed-off-by: Qing Wang > > --- > > mm/vmalloc.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 61caa55a4402..8aebbb51e178 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -2071,6 +2071,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size, > > * to avoid false negatives. > > */ > > kmemleak_scan_area(&va->rb_node, SIZE_MAX, gfp_mask); > > + INIT_LIST_HEAD(&va->list); > > } > > > va->list does not require to be initialized. Because: > > spin_lock(&vn->busy.lock); > insert_vmap_area(va, &vn->busy.root, &vn->busy.head); > spin_unlock(&vn->busy.lock); > > when a node is inserted into list_head, its next/prev pointers are > properly set by the list_add(). > > Or, am i missing something? > > -- > Uladzislau Rezki First, va->list is inserted into the list_head when insert_vmap_area() calls link_va(). However, if find_va_links() returns NULL, link_va() will not be called, leaving va->list uninitialized. Second, even if link_va() is called, list_add() will still invoke __list_add_valid() which reads va->list fields (prev/next). Under KMSAN, this will also report a same uninit-value error. -- Best Regards, Qing