On Sat, Jul 18, 2020 at 04:54:09PM +0800, Hillf Danton wrote: > > Wed, 08 Jul 2020 23:43:19 -0700 > > syzbot found the following crash on: > > > > HEAD commit: e44f65fd xen-netfront: remove redundant assignment to vari.. > > git tree: net-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=15de54a7100000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=829871134ca5e230 > > dashboard link: https://syzkaller.appspot.com/bug?extid=ed318e8b790ca72c5ad0 > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=113406a7100000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=175597d3100000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+ed318e8b790ca72c5ad0@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > > CPU: 1 PID: 1155 Comm: khugepaged Not tainted 5.8.0-rc2-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > RIP: 0010:anon_vma_lock_write include/linux/rmap.h:120 [inline] > > RIP: 0010:collapse_huge_page mm/khugepaged.c:1110 [inline] > > RIP: 0010:khugepaged_scan_pmd mm/khugepaged.c:1349 [inline] > > RIP: 0010:khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline] > > RIP: 0010:khugepaged_do_scan mm/khugepaged.c:2193 [inline] > > RIP: 0010:khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238 > > Code: 01 00 00 48 8d bb 88 00 00 00 48 89 f8 48 c1 e8 03 42 80 3c 30 00 0f 85 fa 0f 00 00 48 8b 9b 88 00 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 d4 0f 00 00 48 8b 3b 48 83 c7 08 e8 9f ff 30 > > RSP: 0018:ffffc90004be7c80 EFLAGS: 00010246 > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81a72d8b > > RDX: ffff8880a69d8100 RSI: ffffffff81b7606b RDI: ffff88809f0577c0 > > RBP: 0000000000000000 R08: 0000000000000000 R09: ffff8881ff213a7f > > R10: 0000000000000080 R11: 0000000000000000 R12: ffffffff8aae6110 > > R13: ffffc90004be7de0 R14: dffffc0000000000 R15: 0000000020000000 > > FS: 0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000000000000 CR3: 00000001fe0cf000 CR4: 00000000001406e0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > kthread+0x3b5/0x4a0 kernel/kthread.c:291 > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293 > > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") It looks sane, but I think it's easier to check in hugepage_vma_revalidate(). Something like this (untested): diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b043c40a21d4..700f5160f3e4 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, return SCAN_ADDRESS_RANGE; if (!hugepage_vma_check(vma, vma->vm_flags)) return SCAN_VMA_CHECK; + /* Anon VMA expected */ + if (!vma->anon_vma || vma->vm_ops) + return SCAN_VMA_CHECK; return 0; } -- Kirill A. Shutemov
