From: Steven Rostedt (VMware) Date: Fri, 28 Jun 2019 01:18:19 +0000 (-0400) Subject: ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare() X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=39611265edc1af3d574178202e19c31e187e7cf2;p=openwrt%2Fstaging%2Fblogic.git 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 Reviewed-by: Josh Poimboeuf Reviewed-by: Petr Mladek Signed-off-by: Steven Rostedt (VMware) --- 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();