Commit 39611265 authored Jun 27, 2019 by Steven Rostedt (VMware)

ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare()

Taking the text_mutex in ftrace_arch_code_modify_prepare() is to fix a
race against module loading and live kernel patching that might try to
change the text permissions while ftrace has it as read/write. This
really needs to be documented in the code. Add a comment that does such.

Link: http://lkml.kernel.org/r/20190627211819.5a591f52@gandalf.local.home

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent d5b844a2

arch/x86/kernel/ftrace.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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();