Re: [PATCH] ftrace: Remove possible deadlock between register_kprobe() and ftrace_run_update_code()

[Steven Rostedt <rostedt@xxxxxxxxxxx>]

On Thu, 27 Jun 2019 18:19:52 -0500
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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();