Is remount racy?
Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cd: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000668-0x000000000000066f]
CPU: 1 UID: 0 PID: 16041 Comm: syz.5.1422 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:txEnd+0xb4/0x530
Code: 49 8d 5e 20 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 6c a3 ca fe 41 bf 68 06 00 00 4c 03 3b 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 4d a3 ca fe 49 8b 1f 48 83 c3 30
RSP: 0018:ffffc90004b7fb00 EFLAGS: 00010202
RAX: 00000000000000cd RBX: ffffc90002a91020 RCX: 0000000000000000
RDX: 0000000000000006 RSI: ffffffff8dfe60aa RDI: 00000000ffffffff
RBP: ffffc90004b7fd68 R08: ffffffff903316f7 R09: 1ffffffff20662de
R10: dffffc0000000000 R11: fffffbfff20662df R12: 1ffff9200096ff70
R13: dffffc0000000000 R14: ffffc90002a91000 R15: 0000000000000668
FS:  00007fced7afe6c0(0000) GS:ffff8882a9218000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd9cb9ff000 CR3: 0000000102346000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 jfs_mknod+0x323/0x9d0
 vfs_mknod+0x441/0x600
 filename_mknodat+0x3cb/0x660
 __se_sys_mknod+0x3a/0x150
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fced6b9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fced7afe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007fced6e16090 RCX: 00007fced6b9ce59
RDX: 000000005d5dfca8 RSI: 0000000000001000 RDI: 0000200000000080
RBP: 00007fced6c32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fced6e16128 R14: 00007fced6e16090 R15: 00007ffee27b76d8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:txEnd+0xb4/0x530
Code: 49 8d 5e 20 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 6c a3 ca fe 41 bf 68 06 00 00 4c 03 3b 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 4d a3 ca fe 49 8b 1f 48 83 c3 30
RSP: 0018:ffffc90004b7fb00 EFLAGS: 00010202
RAX: 00000000000000cd RBX: ffffc90002a91020 RCX: 0000000000000000
RDX: 0000000000000006 RSI: ffffffff8dfe60aa RDI: 00000000ffffffff
RBP: ffffc90004b7fd68 R08: ffffffff903316f7 R09: 1ffffffff20662de
R10: dffffc0000000000 R11: fffffbfff20662df R12: 1ffff9200096ff70
R13: dffffc0000000000 R14: ffffc90002a91000 R15: 0000000000000668
FS:  00007fced7afe6c0(0000) GS:ffff8882a9218000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd9cb9ff000 CR3: 0000000102346000 CR4: 00000000000006f0
