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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Johannes Erdfelt <johannes@erdfelt.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Jessica Yu <jeyu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>, Ingo Molnar <mingo@redhat.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Oops caused by race between livepatch and ftrace
Date: Tue, 21 May 2019 09:16:29 -0500	[thread overview]
Message-ID: <20190521141629.bmk5onsaab26qoaw@treble> (raw)
In-Reply-To: <20190520173910.6da9ddaf@gandalf.local.home>

On Mon, May 20, 2019 at 05:39:10PM -0400, Steven Rostedt wrote:
> On Mon, 20 May 2019 16:19:31 -0500
> Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index a12aff849c04..8259d4ba8b00 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -34,6 +34,7 @@
> >  #include <linux/hash.h>
> >  #include <linux/rcupdate.h>
> >  #include <linux/kprobes.h>
> > +#include <linux/memory.h>
> >  
> >  #include <trace/events/sched.h>
> >  
> > @@ -2610,10 +2611,12 @@ static void ftrace_run_update_code(int command)
> >  {
> >  	int ret;
> >  
> > +	mutex_lock(&text_mutex);
> > +
> 
> Hmm, this may blow up with lockdep, as I believe we already have a
> locking dependency of:
> 
>  text_mutex -> ftrace_lock
> 
> And this will reverses it. (kprobes appears to take the locks in this
> order).
> 
> Perhaps have live kernel patching grab ftrace_lock?

Where does kprobes call into ftrace with the text_mutex?  I couldn't
find it.

-- 
Josh

  reply	other threads:[~2019-05-21 14:16 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20 19:49 Johannes Erdfelt
2019-05-20 20:46 ` Joe Lawrence
2019-05-20 21:09   ` Johannes Erdfelt
2019-05-20 21:19     ` Josh Poimboeuf
2019-05-20 21:39       ` Steven Rostedt
2019-05-21 14:16         ` Josh Poimboeuf [this message]
2019-05-21 14:42           ` Steven Rostedt
2019-05-21 16:42             ` Josh Poimboeuf
2019-05-21 16:53               ` Steven Rostedt
2019-05-29 11:17                 ` Jiri Kosina
2019-05-29 12:06                   ` Steven Rostedt
2019-05-29 12:30                     ` Josh Poimboeuf
2019-05-22 13:00               ` Josh Poimboeuf
2019-05-29 17:29               ` Jessica Yu
2019-05-29 17:39                 ` Josh Poimboeuf
2019-05-29 18:34                   ` Jessica Yu
2019-05-20 21:48       ` Johannes Erdfelt
2019-05-20 21:19     ` Joe Lawrence
2019-05-21 19:27       ` Joe Lawrence
2019-05-21 21:00         ` Josh Poimboeuf

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