Is remount racy?
general protection fault, probably for non-canonical address 0xdffffc00000000cf: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000678-0x000000000000067f]
CPU: 1 PID: 8024 Comm: syz.3.772 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:JFS_SBI fs/jfs/jfs_incore.h:217 [inline]
RIP: 0010:txEnd+0xb0/0x520 fs/jfs/jfs_txnmgr.c:507
Code: 49 8d 5e 20 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 40 09 e3 fe 41 bf 78 06 00 00 4c 03 3b 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 21 09 e3 fe 49 8b 1f 48 83 c3 30
RSP: 0018:ffffc9000c52fb20 EFLAGS: 00010206
RAX: 00000000000000cf RBX: ffffc90002699020 RCX: 1ffff920018a5f48
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: 00000000ffffffff
RBP: ffffc9000c52fda0 R08: dffffc0000000000 R09: fffffbfff2119052
R10: fffffbfff2119052 R11: 1ffffffff2119051 R12: 1ffff920018a5f74
R13: dffffc0000000000 R14: ffffc90002699000 R15: 0000000000000678
FS:  00007f6ffd8166c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6ff2e1d000 CR3: 0000000076bc5000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 jfs_mknod+0x2e9/0x930 fs/jfs/namei.c:1428
 vfs_mknod+0x424/0x4c0 fs/namei.c:3993
 do_mknodat+0x34e/0x4c0 fs/namei.c:-1
 __do_sys_mknod fs/namei.c:4076 [inline]
 __se_sys_mknod fs/namei.c:4074 [inline]
 __x64_sys_mknod+0x8a/0xa0 fs/namei.c:4074
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6ffc98f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6ffd816038 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007f6ffcbe5fa0 RCX: 00007f6ffc98f749
RDX: 0000000000000000 RSI: 0000000008001420 RDI: 0000200000000040
RBP: 00007f6ffca13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6ffcbe6038 R14: 00007f6ffcbe5fa0 R15: 00007fff98f15dd8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:JFS_SBI fs/jfs/jfs_incore.h:217 [inline]
RIP: 0010:txEnd+0xb0/0x520 fs/jfs/jfs_txnmgr.c:507
Code: 49 8d 5e 20 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 40 09 e3 fe 41 bf 78 06 00 00 4c 03 3b 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 21 09 e3 fe 49 8b 1f 48 83 c3 30
RSP: 0018:ffffc9000c52fb20 EFLAGS: 00010206
RAX: 00000000000000cf RBX: ffffc90002699020 RCX: 1ffff920018a5f48
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: 00000000ffffffff
RBP: ffffc9000c52fda0 R08: dffffc0000000000 R09: fffffbfff2119052
R10: fffffbfff2119052 R11: 1ffffffff2119051 R12: 1ffff920018a5f74
R13: dffffc0000000000 R14: ffffc90002699000 R15: 0000000000000678
FS:  00007f6ffd8166c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6ff2e1d000 CR3: 0000000076bc5000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	49 8d 5e 20          	lea    0x20(%r14),%rbx
   4:	48 89 d8             	mov    %rbx,%rax
   7:	48 c1 e8 03          	shr    $0x3,%rax
   b:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
  10:	74 08                	je     0x1a
  12:	48 89 df             	mov    %rbx,%rdi
  15:	e8 40 09 e3 fe       	call   0xfee3095a
  1a:	41 bf 78 06 00 00    	mov    $0x678,%r15d
  20:	4c 03 3b             	add    (%rbx),%r15
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 ff             	mov    %r15,%rdi
  34:	e8 21 09 e3 fe       	call   0xfee3095a
  39:	49 8b 1f             	mov    (%r15),%rbx
  3c:	48 83 c3 30          	add    $0x30,%rbx