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BUG: KASAN: use-after-free in btrfs_printk+0x38b/0x40c fs/btrfs/super.c:245
Read of size 8 at addr ffff888013ff46a0 by task systemd-udevd/8573

CPU: 1 PID: 8573 Comm: systemd-udevd Not tainted 5.10.0-rc1-next-20201030-syzkaller #0
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+0x107/0x163 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 btrfs_printk+0x38b/0x40c fs/btrfs/super.c:245
 device_list_add.cold+0x99/0x31e fs/btrfs/volumes.c:943
 btrfs_scan_one_device+0x339/0x4a0 fs/btrfs/volumes.c:1366
 btrfs_control_ioctl+0x12a/0x2d0 fs/btrfs/super.c:2327
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f38d837e017
Code: 00 00 00 48 8b 05 81 7e 2b 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 51 7e 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffebc6f0948 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f38d837e017
RDX: 00007ffebc6f0960 RSI: 0000000090009427 RDI: 000000000000000f
RBP: 00007ffebc6f0960 R08: 0000000000000000 R09: 0000000000000030
R10: 0000000000000001 R11: 0000000000000246 R12: 000000000000000f
R13: 0000000000000000 R14: 000055df9c3758c0 R15: 000055df9c35b060

The buggy address belongs to the page:
page:0000000076aa2c1a refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x13ff4
flags: 0xfff00000000000()
raw: 00fff00000000000 ffffea0000be3a08 ffffea0000529b08 0000000000000000
raw: 0000000000000000 0000000000000002 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888013ff4580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888013ff4600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888013ff4680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff888013ff4700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888013ff4780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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