From: Steven Rostedt <rostedt@goodmis.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
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: Mon, 20 May 2019 17:39:10 -0400 [thread overview]
Message-ID: <20190520173910.6da9ddaf@gandalf.local.home> (raw)
In-Reply-To: <20190520211931.vokbqxkx5kb6k2bz@treble>
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?
-- Steve
> ret = ftrace_arch_code_modify_prepare();
> FTRACE_WARN_ON(ret);
> if (ret)
> - return;
> + goto out_unlock;
>
> /*
> * By default we use stop_machine() to modify the code.
> @@ -2625,6 +2628,9 @@ static void ftrace_run_update_code(int command)
>
> ret = ftrace_arch_code_modify_post_process();
> FTRACE_WARN_ON(ret);
> +
> +out_unlock:
> + mutex_unlock(&text_mutex);
> }
>
> static void ftrace_run_modify_code(struct ftrace_ops *ops, int command,
> @@ -5776,6 +5782,7 @@ void ftrace_module_enable(struct module *mod)
> struct ftrace_page *pg;
>
> mutex_lock(&ftrace_lock);
> + mutex_lock(&text_mutex);
>
> if (ftrace_disabled)
> goto out_unlock;
> @@ -5837,6 +5844,7 @@ void ftrace_module_enable(struct module *mod)
> ftrace_arch_code_modify_post_process();
>
> out_unlock:
> + mutex_unlock(&text_mutex);
> mutex_unlock(&ftrace_lock);
>
> process_cached_mods(mod->name);
next prev parent reply other threads:[~2019-05-20 21:39 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 19:49 Oops caused by race between livepatch and ftrace 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 [this message]
2019-05-21 14:16 ` Josh Poimboeuf
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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