From: Miroslav Benes <mbenes@suse.cz>
To: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
Masami Hiramatsu <mhiramat@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jiri Kosina <jikos@kernel.org>,
Joe Lawrence <joe.lawrence@redhat.com>,
live-patching@vger.kernel.org
Subject: Re: [PATCH 6/9] livepatch/ftrace: Add recursion protection to the ftrace callback
Date: Thu, 29 Oct 2020 16:03:09 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.2010291601510.1688@pobox.suse.cz> (raw)
In-Reply-To: <20201029145709.GD16774@alley>
On Thu, 29 Oct 2020, Petr Mladek wrote:
> On Thu 2020-10-29 14:51:06, Miroslav Benes wrote:
> > On Wed, 28 Oct 2020, Steven Rostedt wrote:
>
> > Hm, I've always thought that we did not need any kind of recursion
> > protection for our callback. It is marked as notrace and it does not call
> > anything traceable. In fact, it does not call anything. I even have a note
> > in my todo list to mark the callback as RECURSION_SAFE :)
>
> Well, it calls WARN_ON_ONCE() ;-)
Oh my, I learned to ignore these. Of course there is printk hidden
everywhere.
> > At the same time, it probably does not hurt and the patch is still better
> > than what we have now without RECURSION_SAFE if I understand the patch set
> > correctly.
>
> And better be on the safe side.
Agreed.
> > > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > > Cc: Jiri Kosina <jikos@kernel.org>
> > > Cc: Miroslav Benes <mbenes@suse.cz>
> > > Cc: Petr Mladek <pmladek@suse.com>
> > > Cc: Joe Lawrence <joe.lawrence@redhat.com>
> > > Cc: live-patching@vger.kernel.org
> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > > ---
> > > kernel/livepatch/patch.c | 5 +++++
> > > 1 file changed, 5 insertions(+)
> > >
> > > diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> > > index b552cf2d85f8..6c0164d24bbd 100644
> > > --- a/kernel/livepatch/patch.c
> > > +++ b/kernel/livepatch/patch.c
> > > @@ -45,9 +45,13 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> > > struct klp_ops *ops;
> > > struct klp_func *func;
> > > int patch_state;
> > > + int bit;
> > >
> > > ops = container_of(fops, struct klp_ops, fops);
> > >
> > > + bit = ftrace_test_recursion_trylock();
> > > + if (bit < 0)
> > > + return;
> >
> > This means that the original function will be called in case of recursion.
> > That's probably fair, but I'm wondering if we should at least WARN about
> > it.
>
> Yeah, the early return might break the consistency model and
> unexpected things might happen. We should be aware of it.
> Please use:
>
> if (WARN_ON_ONCE(bit < 0))
> return;
>
> WARN_ON_ONCE() might be part of the recursion. But it should happen
> only once. IMHO, it is worth the risk.
Agreed.
Miroslav
next prev parent reply other threads:[~2020-10-29 15:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201028115244.995788961@goodmis.org>
2020-10-28 11:52 ` [PATCH 6/9] livepatch/ftrace: Add recursion protection to the ftrace callback Steven Rostedt
2020-10-29 13:51 ` Miroslav Benes
2020-10-29 14:37 ` Steven Rostedt
2020-10-30 12:28 ` Steven Rostedt
2020-10-29 14:57 ` Petr Mladek
2020-10-29 15:03 ` Miroslav Benes [this message]
2020-10-29 18:24 ` Steven Rostedt
2020-10-30 9:48 ` Miroslav Benes
2020-10-30 10:41 ` Petr Mladek
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