Re: [PATCH] uprobes: Free utask on dup_return_instance() failure

[Andrii Nakryiko]

On Tue, Aug 25, 2026 at 5:27 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> On 08/24, Andrii Nakryiko wrote:
> >
> > On Mon, Aug 24, 2026 at 8:57 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > >
> > > force_exit_sig(SIGILL) can't be ignored too. But I am fine either way.
> >
> > Current SIGILL sending is already pretty bad behavior that bites us
> > periodically, instead of doubling down on killing the user space
> > process because something about installing uprobe goes wrong, let's
> > think about a bit less destructive way to do this. Mark uprobe for a
> > particular process as defunct or "detaching it", or something along
> > those lines. But not just kill innocent processes.
>
> Well. Yes, SIGILL sending acts as BUG_ON(), this is not nice and

The problem is that this is actually not a bug but a very real and
expected behavior with user-space using fibers or coroutines. Any
suggestions how we can make this less violent, as it's actually quite
dangerous and kills production applications when someone (unknowingly)
tries to uretprobe trace them...

> probably we can improve the current code. And, just in case, as for
> uprobe_copy_process() in particular I agree that Option B (make fork()
> fail) is better.
>
> But what, say, uprobe_handle_trampoline() can do if ->return_instances
> is NULL? Either we have a kernel bug, or the probed task does something
> wrong. In both cases it is better to kill the task with pr_warn() and
> generate the core dump.

I don't remember all the code paths, but just shooting in the dark
there, we can always poison a pointer to distinguish or something? or
just assume kernel bugs do not happen and ignore NULL. Or something
along those lines.

>
> Oleg.
>