Re: [syzbot] [mm] WARNING in get_pte_pfn

[Yu Zhao <yuzhao@google.com>]

On Fri, Dec 22, 2023 at 12:11:21AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0e389834672c Merge tag 'for-6.7-rc5-tag' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1454824ee80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f21aff374937e60e
> dashboard link: https://syzkaller.appspot.com/bug?extid=03fd9b3f71641f0ebf2d
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13b4ef49e80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=118314d6e80000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e58cd74e152a/disk-0e389834.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/45d17ccb34bc/vmlinux-0e389834.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b9b7105d4e08/bzImage-0e389834.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+03fd9b3f71641f0ebf2d@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 5066 at mm/vmscan.c:3242 get_pte_pfn+0x1b5/0x3f0 mm/vmscan.c:3242
> Modules linked in:
> CPU: 1 PID: 5066 Comm: syz-executor668 Not tainted 6.7.0-rc5-syzkaller-00270-g0e389834672c #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> RIP: 0010:get_pte_pfn+0x1b5/0x3f0 mm/vmscan.c:3242
> Code: f3 74 2a e8 6d 78 cb ff 31 ff 48 b8 00 00 00 00 00 00 00 02 48 21 c5 48 89 ee e8 e6 73 cb ff 48 85 ed 74 4e e8 4c 78 cb ff 90 <0f> 0b 90 48 c7 c3 ff ff ff ff e8 3c 78 cb ff 48 b8 00 00 00 00 00
> RSP: 0018:ffffc900041e6878 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 000000000007891d RCX: ffffffff81bbf6e3
> RDX: ffff88807d813b80 RSI: ffffffff81bbf684 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000200 R11: 0000000000000003 R12: 0000000000000200
> R13: 1ffff9200083cd0f R14: 0000000000010b21 R15: 0000000020ffc000
> FS:  0000555555f4d480(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000005fbfa000 CR4: 0000000000350ef0
> Call Trace:
>  <TASK>
>  lru_gen_look_around+0x70d/0x11a0 mm/vmscan.c:4001
>  folio_referenced_one+0x5a2/0xf70 mm/rmap.c:843
>  rmap_walk_anon+0x225/0x570 mm/rmap.c:2485
>  rmap_walk mm/rmap.c:2562 [inline]
>  rmap_walk mm/rmap.c:2557 [inline]
>  folio_referenced+0x28a/0x4b0 mm/rmap.c:960
>  folio_check_references mm/vmscan.c:829 [inline]
>  shrink_folio_list+0x1ace/0x3f00 mm/vmscan.c:1160
>  evict_folios+0x6e7/0x1b90 mm/vmscan.c:4499
>  try_to_shrink_lruvec+0x638/0xa10 mm/vmscan.c:4704
>  lru_gen_shrink_lruvec mm/vmscan.c:4849 [inline]
>  shrink_lruvec+0x314/0x2990 mm/vmscan.c:5622
>  shrink_node_memcgs mm/vmscan.c:5842 [inline]
>  shrink_node+0x811/0x3710 mm/vmscan.c:5877
>  shrink_zones mm/vmscan.c:6116 [inline]
>  do_try_to_free_pages+0x36c/0x1940 mm/vmscan.c:6178

#syz test

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9dd8977de5a2..041f9ad8f95b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3230,7 +3230,8 @@ static bool get_next_vma(unsigned long mask, unsigned long size, struct mm_walk
 	return false;
 }
 
-static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned long addr)
+static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned long addr,
+				 struct page *page)
 {
 	unsigned long pfn = pte_pfn(pte);
 
@@ -3239,8 +3240,14 @@ static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned
 	if (!pte_present(pte) || is_zero_pfn(pfn))
 		return -1;
 
-	if (WARN_ON_ONCE(pte_devmap(pte) || pte_special(pte)))
+	if (pte_devmap(pte) || pte_special(pte)) {
+		if (page)
+			dump_page(page, "get_pte_pfn()");
+		dump_vma(vma);
+		dump_mm(vma->vm_mm);
+		BUG();
 		return -1;
+	}
 
 	if (WARN_ON_ONCE(!pfn_valid(pfn)))
 		return -1;
@@ -3331,7 +3338,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 		total++;
 		walk->mm_stats[MM_LEAF_TOTAL]++;
 
-		pfn = get_pte_pfn(ptent, args->vma, addr);
+		pfn = get_pte_pfn(ptent, args->vma, addr, NULL);
 		if (pfn == -1)
 			continue;
 
@@ -3998,7 +4005,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 		unsigned long pfn;
 		pte_t ptent = ptep_get(pte + i);
 
-		pfn = get_pte_pfn(ptent, pvmw->vma, addr);
+		pfn = get_pte_pfn(ptent, pvmw->vma, addr, pfn_to_page(pvmw->pfn));
 		if (pfn == -1)
 			continue;