linux-kernel - Re: [PATCH 2/8] uprobes: revamp uprobe refcounting and lifetime management

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Message-ID: <CAEf4BzY7fBZBJo3PGaDLp6yzpi7S9QTkcirP+Nz03rL2wcU-0A@mail.gmail.com>
Date: Fri, 2 Aug 2024 07:58:55 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-trace-kernel@...r.kernel.org, 
	peterz@...radead.org, rostedt@...dmis.org, mhiramat@...nel.org, 
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, jolsa@...nel.org, 
	paulmck@...nel.org
Subject: Re: [PATCH 2/8] uprobes: revamp uprobe refcounting and lifetime management

On Fri, Aug 2, 2024 at 1:50 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> On 08/01, Andrii Nakryiko wrote:
> >
> > > +               /* TODO : cant unregister? schedule a worker thread */
> > > +               WARN(err, "leaking uprobe due to failed unregistration");
>
> > Ok, so now that I added this very loud warning if
> > register_for_each_vma(uprobe, NULL) returns error, it turns out it's
> > not that unusual for this unregistration to fail.
>
> ...
>
> > So, is there something smarter we can do in this case besides leaking
> > an uprobe (and note, my changes don't change this behavior)?
>
> Something like schedule_work() which retries register_for_each_vma()...

And if that fails again, what do we do? Because I don't think we even
need schedule_work(), we can just keep some list of "pending to be
retried" items and check them after each
uprobe_register()/uprobe_unregister() call. I'm just not clear how we
should handle stubborn cases (but honestly I haven't even tried to
understand all the details about this just yet).

>
> > I can of course just drop the WARN given it's sort of expected now,
>
> Or least replace it with pr_warn() or uprobe_warn(), WARN() certainly
> makes no sense imo...
>

ok, makes sense, will change to uprobe_warn()

> > I don't
> > think that should block optimization work, but just something to keep
> > in mind and maybe fix as a follow up.
>
> Agreed, lets do this separately.
>

yep

> Oleg.
>