On Mon, Jan 7, 2019 at 1:52 AM syzbot
[off-list ref] wrote:

Hello,

syzbot found the following crash on:

HEAD commit:    574823bfab82 Change mincore() to count "mapped" pages rath..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=121dc980c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d55557b516c45456
dashboard link: https://syzkaller.appspot.com/bug?extid=23f5ac6e7c0b6cc63734
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+23f5ac6e7c0b6cc63734@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(class_idx > MAX_LOCKDEP_KEYS)
WARNING: CPU: 1 PID: 30980 at kernel/locking/lockdep.c:3315
__lock_acquire+0x14cd/0x4a30 kernel/locking/lockdep.c:3315
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 30980 Comm: syz-executor5 Not tainted 4.20.0+ #13
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1db/0x2d0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x48 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  fixup_bug arch/x86/kernel/traps.c:173 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:__lock_acquire+0x14cd/0x4a30 kernel/locking/lockdep.c:3315
Code: 8b 1d 3b eb f7 08 45 85 db 0f 85 f0 f3 ff ff 48 c7 c6 60 a1 4b 88 48
c7 c7 80 76 4b 88 44 89 9c 24 98 00 00 00 e8 f3 5f e7 ff <0f> 0b 44 8b 9c
24 98 00 00 00 e9 c9 f3 ff ff 8b 0d 2e 9c f2 09 85
RSP: 0018:ffff8880710cf0c0 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 00000000fffe4386 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81684ce6 RDI: 0000000000000006
RBP: ffff8880710cf350 R08: ffff888081d582c0 R09: fffffbfff1333299
R10: fffffbfff1333298 R11: ffffffff899994c3 R12: ffff888081d582c0
R13: ffff888081d58b8a R14: 0000000000000001 R15: 00000000fffe4386
kobject: 'kvm' (00000000d564ee4d): kobject_uevent_env
  lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3841
kobject: 'kvm' (00000000d564ee4d): fill_kobj_path: path
= '/devices/virtual/misc/kvm'
  __raw_write_lock_bh include/linux/rwlock_api_smp.h:203 [inline]
  _raw_write_lock_bh+0x33/0x50 kernel/locking/spinlock.c:312
  sock_orphan include/net/sock.h:1796 [inline]

This is probably a consequence of the use-after-free bug,
so:

#syz dup: WARNING: refcount bug in nr_release