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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2019-06-27 21:18:19 -0400
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-06-28 14:21:25 -0400
commit39611265edc1af3d574178202e19c31e187e7cf2 (patch)
tree5a2fb0590d8da026037129d73500754edceedbc8 /arch
parentd5b844a2cf507fc7642c9ae80a9d585db3065c28 (diff)
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/ftrace.c5
1 files changed, 5 insertions, 0 deletions
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();