Re: [PATCH 0/4] vmcore-tasks: export per-task metadata to vmcoreinfo

[Baoquan He]

On 07/20/26 at 10:35am, Omar Sandoval wrote:
> On Mon, Jul 20, 2026 at 10:40:43PM +0800, Baoquan He wrote:
> > On 07/20/26 at 03:43pm, Mike Rapoport wrote:
> > > Hi Simon,
> > > 
> > > On Mon, Jul 20, 2026 at 10:19:27AM +0100, Simon Horman wrote:
> > > > On Tue, Jul 07, 2026 at 09:21:58AM +0300, Mike Rapoport wrote:
> > > > > On Tue, Jun 23, 2026 at 12:14:26AM +0300, Pnina Feder wrote:
> > > > > > This series extends vmcoreinfo with struct offsets and sizes needed by
> > > > > > the vmcore-tasks userspace tool to extract per-task state from a vmcore
> > > > > > dump without requiring kernel debug symbols (DWARF/BTF).
> > > > > > 
> > > > > > The vmcore-tasks tool reads /proc/vmcore (or a saved vmcore file) and
> > > > > > reconstructs, for each task:
> > > > > >   - task name, pid, state, flags
> > > > > >   - VMA list (start, end, flags, backing file)
> > > > > >   - user register state (saved on the kernel stack at kernel entry)
> > > > > >   - user-space backtrace with VMA/filename mapping
> > > > > >   - kernel dmesg buffer
> > > > > > 
> > > > > > This provides a lightweight post-mortem crash analysis capability for
> > > > > > production environments where full debug info (DWARF/BTF) is not
> > > > > > available.
> > > > > > 
> > > > > > The companion userspace tool is submitted to kexec-tools:
> > > > > >   https://lore.kernel.org/all/20260622205550.1087163-1-pnina.feder@xxxxxxxxxxxx/
> > > > > 
> > > > > Sorry for the delay, this fell between the cracks somehow.
> > > > > 
> > > > > The kernel side looks fine overall, but to merge it there should be an
> > > > > agreement from the userspace side maintainers that vmcore-tasks is
> > > > > something they are wishing to accept.
> > > > 
> > > > Hi Mike, all,
> > > > 
> > > > Sorry for the extended delay.
> > > > 
> > > > I will send some minor feedback to the user-space tool patchset
> > > > but overall, yes, this is something I would be happy to accept.
> > > > 
> > > > I don't want to create a chicken-and-egg type problem here.
> > > > But it's probably worth mentioning that usually features
> > > > hit the kernel before the corresponding code is accepted
> > > > into kexec-tools.
> > > 
> > > Sorry if I wasn't clear. 
> > > 
> > > I didn't mean that the feature should be merged into kexec-tools before
> > > merging the kernel bits. I just wanted to make sure there's no fundamental
> > > issue from kexec-tools perspective.
> > > 
> > > > Let me know how you would like to proceed.
> > > 
> > > I'm going to wait for Baoquan's review and once that's done I'll pick up
> > > the kernel bits.
> > 
> > Oh, sorry, I just noticed this series, but a quick look give me a hint
> > of 'No, I don't like it.' We have had Crash utility, Drgn, now a new one
> > comes up. I have some concerns to Pnina:
> > 
> > 1. Exporting maple tree internals (maple_node, maple_range_64,
> >    maple_arange_64, maple_metadata) as vmcoreinfo ABI is problematic.
> >    These are private implementation details, not stable structures like
> >    task_struct. Any refactoring of the maple tree will silently break
> >    the userspace tool. 
> > 
> > 2. Without DWARF/BTF, the debugging scope is inherently limited — no
> >    kernel stack backtrace, no symbol resolution, no variable access.
> >    That's essentially "ps + /proc/PID/maps" from a vmcore. Have you
> >    considered enabling CONFIG_DEBUG_INFO_BTF on your platforms instead?
> >    BTF is compact (typically < 1 MB) and would give drgn full access
> >    without needing vmlinux debug packages. That seems like a better
> >    return-on-investment than maintaining ~40 new vmcoreinfo exports.
> > 
> > 3. Beyond the technical concerns, I wonder about adoption. vmcore-tasks
> >    targets a fairly narrow use case — platforms without DWARF/BTF, where
> >    you still have vmcore but can't ship vmlinux. Is Mobileye currently
> >    the only consumer? Are you guys already using it widely and fully?
> >    If this lands but doesn't see broader uptake, the ~40 exports risk
> >    becoming dead weight in vmcoreinfo — nobody actively uses them, but
> >    kernel changes still need to keep them consistent, or they silently
> >    rot and give users wrong results. 
> > 
> > Regards,
> > Baoquan
> 
> (Adding linux-debuggers mailing list).
> 
> I agree with all of Baoquan's points here, with a couple of notes:
> 
> 1. drgn's BTF support is currently a work in progress, but it's shaping
>    up well: https://github.com/osandov/drgn/pull/625.
> 2. makedumpfile is also gaining BTF extension support:
>    https://lore.kernel.org/all/20260617051834.95404-1-ltao@xxxxxxxxxx/.
>    It's lighter-weight than drgn while still being much more general
>    than this series.

Thanks for adding the information, very helpful.