How to resolve 'MNT_NOSUID not defined' in vmlinux-gdb.py when debugging the Linux kernel with GDB

Hit a NameError loading vmlinux-gdb.py in GDB? MNT_NOSUID isn't Python; fix the helper's parsing with the LKML patch and restore Linux kernel debugging.

Debugging a Linux kernel with GDB often starts with loading helper logic from vmlinux-gdb.py. Sometimes it fails right at the entry point with a Python NameError about MNT_NOSUID not being defined. If that’s what you see, the issue isn’t in your Python environment. It’s about a kernel flag that the script stumbles on while parsing.

Reproducing the error

The failure is triggered as soon as the helper is sourced in GDB:

(gdb) source vmlinux-gdb.py
Python Exception <class 'NameError'>: name 'MNT_NOSUID' is not defined
Error occurred in Python: name 'MNT_NOSUID' is not defined

What’s actually going on

MNT_NOSUID is a kernel flag that means the filesystem should be mounted with the constraint that setuid and setgid programs referenced through this mount must not be executable. In other words, it represents the nosuid behavior in the kernel’s view of a mount.

It is not a Python symbol and it is not supposed to come from a Python package. The error comes from the helper script tripping over this flag when parsing, which makes the symbol effectively unparseable in that context. This is a known issue and it has been discussed publicly; see the LKML thread: https://lkml.org/lkml/2025/5/31/383.

Fix that resolves the failure

The resolution is to apply the patch referenced in the LKML discussion. After applying the fix locally, the helper loads as expected; for example, it was applied on a v6.16 setup and worked, and after applying the patch the script loaded successfully.

Once the fix is in place, the same GDB command no longer throws the exception:

(gdb) source vmlinux-gdb.py

Why this matters for kernel debugging

Without the helper, a lot of quality-of-life features in kernel debugging are unavailable, and you can end up misdirected into chasing nonexistent Python dependencies. Recognizing that MNT_NOSUID is a kernel mount flag clarifies that the problem is within the helper’s parsing logic, not your userspace setup, distribution, or the VM environment.

Takeaways

If sourcing vmlinux-gdb.py fails with “name 'MNT_NOSUID' is not defined,” treat MNT_NOSUID as what it is: a Linux kernel mount flag, not a Python object. Consult the LKML thread, apply the provided patch, and reload the helper. Once the fix is applied, the script should load cleanly, and you can proceed with kernel debugging without detours.