linux-kernel - Re: [PATCH] ftrace: Remove possible deadlock between register_kprobe() and ftrace_run_update

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Date:   Thu, 27 Jun 2019 21:13:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Miroslav Benes <mbenes@...e.cz>, Jessica Yu <jeyu@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Johannes Erdfelt <johannes@...felt.com>,
        Ingo Molnar <mingo@...nel.org>, mhiramat@...nel.org,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH] ftrace: Remove possible deadlock between
 register_kprobe() and ftrace_run_update_code()

On Thu, 27 Jun 2019 18:19:52 -0500
Josh Poimboeuf <jpoimboe@...hat.com> wrote:


> Maybe a comment or two would help though.
> 

I'm adding the following change.  Care to add a "reviewed-by" for this
one?

-- Steve

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 33786044d5ac..d7e93b2783fd 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -36,6 +36,11 @@
 
 int ftrace_arch_code_modify_prepare(void)
 {
+	/*
+	 * Need to grab text_mutex to prevent a race from module loading
+	 * and live kernel patching from changing the text permissions while
+	 * ftrace has it set to "read/write".
+	 */
 	mutex_lock(&text_mutex);
 	set_kernel_text_rw();
 	set_all_modules_text_rw();