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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 ffff88802a9106a0 by task syz-executor.5/4099

CPU: 0 PID: 4099 Comm: syz-executor.5 Not tainted 5.10.0-rc1-next-20201102-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_mount_root+0x4d5/0xbb0 fs/btrfs/super.c:1634
 legacy_get_tree+0x105/0x220 fs/fs_context.c:592
 vfs_get_tree+0x89/0x2f0 fs/super.c:1549
 fc_mount fs/namespace.c:983 [inline]
 vfs_kern_mount.part.0+0xd3/0x170 fs/namespace.c:1013
 vfs_kern_mount+0x3c/0x60 fs/namespace.c:1000
 btrfs_mount+0x234/0xa60 fs/btrfs/super.c:1732
 legacy_get_tree+0x105/0x220 fs/fs_context.c:592
 vfs_get_tree+0x89/0x2f0 fs/super.c:1549
 do_new_mount fs/namespace.c:2896 [inline]
 path_mount+0x12ae/0x1e70 fs/namespace.c:3227
 do_mount fs/namespace.c:3240 [inline]
 __do_sys_mount fs/namespace.c:3448 [inline]
 __se_sys_mount fs/namespace.c:3425 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x46090a
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 ad 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 8a 89 fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007f8f4a8b8a88 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f8f4a8b8b20 RCX: 000000000046090a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f8f4a8b8ae0
RBP: 00007f8f4a8b8ae0 R08: 00007f8f4a8b8b20 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000020000000
R13: 0000000020000100 R14: 0000000020000200 R15: 0000000020016800

The buggy address belongs to the page:
page:00000000568e1139 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x2a910
flags: 0xfff00000000000()
raw: 00fff00000000000 ffffea000073ca08 ffffea0000a44e08 0000000000000000
raw: 0000000000000000 0000000000000002 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88802a910580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88802a910600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88802a910680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff88802a910700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88802a910780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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