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From: Steven Rostedt <rostedt@goodmis.org>
To: Miroslav Benes <mbenes@suse.cz>
Cc: 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>, Petr Mladek <pmladek@suse.com>,
	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 10:37:44 -0400	[thread overview]
Message-ID: <20201029103744.0f7f52dc@gandalf.local.home> (raw)
In-Reply-To: <alpine.LSU.2.21.2010291443310.1688@pobox.suse.cz>

On Thu, 29 Oct 2020 14:51:06 +0100 (CET)
Miroslav Benes <mbenes@suse.cz> wrote:

> > 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.

It's probably what happens today. But if you add a WARN_ON_ONCE() it may
not hurt.

I also plan on adding code that reports when recursion has happened,
because even if it's not a problem, recursion adds extra overhead.

-- Steve

  reply	other threads:[~2020-10-29 14:37 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-28 11:52 [PATCH 0/9] ftrace: Have callbacks handle their own recursion Steven Rostedt
2020-10-28 11:52 ` [PATCH 1/9] ftrace: Move the recursion testing into global headers Steven Rostedt
2020-10-30  9:13   ` Miroslav Benes
2020-10-30 12:30     ` Steven Rostedt
2020-10-28 11:52 ` [PATCH 2/9] ftrace: Add ftrace_test_recursion_trylock() helper function Steven Rostedt
2020-10-28 11:52 ` [PATCH 3/9] ftrace: Optimize testing what context current is in Steven Rostedt
2020-10-28 11:52 ` [PATCH 4/9] pstore/ftrace: Add recursion protection to the ftrace callback Steven Rostedt
2020-10-28 15:59   ` Kees Cook
2020-10-28 11:52 ` [PATCH 5/9] kprobes/ftrace: " Steven Rostedt
2020-10-28 11:52   ` Steven Rostedt
2020-10-29  7:58   ` Masami Hiramatsu
2020-10-29  7:58     ` Masami Hiramatsu
2020-10-29 13:40     ` Steven Rostedt
2020-10-29 13:40       ` Steven Rostedt
2020-11-02  5:08       ` Masami Hiramatsu
2020-11-02  5:08         ` Masami Hiramatsu
2020-10-28 11:52 ` [PATCH 6/9] livepatch/ftrace: " Steven Rostedt
2020-10-29 13:51   ` Miroslav Benes
2020-10-29 14:37     ` Steven Rostedt [this message]
2020-10-30 12:28       ` Steven Rostedt
2020-10-29 14:57     ` Petr Mladek
2020-10-29 15:03       ` Miroslav Benes
2020-10-29 18:24       ` Steven Rostedt
2020-10-30  9:48         ` Miroslav Benes
2020-10-30 10:41           ` Petr Mladek
2020-10-28 11:52 ` [PATCH 7/9] perf/ftrace: " Steven Rostedt
2020-10-28 11:52 ` [PATCH 8/9] perf/ftrace: Check for rcu_is_watching() in callback function Steven Rostedt
2020-10-28 11:52 ` [PATCH 9/9] ftrace: Reverse what the RECURSION flag means in the ftrace_ops Steven Rostedt

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