From 37a756af580f7066b18f60b2693c41604e3268b9 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Wed, 19 Mar 2014 10:01:29 -0500
Subject: [PATCH] kmod/core: protect kpatch_[un]register with mutex

Use a mutex in the register/unregister functions to protect changes to
kpatch_num_registered, kpatch_func_hash and calls to the ftrace
functions by other register/unregister invocations.
---
 kmod/core/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kmod/core/core.c b/kmod/core/core.c
index db82ebb..225c227 100644
--- a/kmod/core/core.c
+++ b/kmod/core/core.c
@@ -48,6 +48,8 @@
 #define KPATCH_HASH_BITS 8
 DEFINE_HASHTABLE(kpatch_func_hash, KPATCH_HASH_BITS);
 
+DEFINE_SEMAPHORE(kpatch_mutex);
+
 static int kpatch_num_registered;
 
 struct kpatch_backtrace_args {
@@ -209,6 +211,8 @@ int kpatch_register(struct module *mod, struct kpatch_func *funcs,
 		.num_funcs = num_funcs,
 	};
 
+	down(&kpatch_mutex);
+
 	for (i = 0; i < num_funcs; i++) {
 		struct kpatch_func *func = &funcs[i];
 
@@ -225,7 +229,7 @@ int kpatch_register(struct module *mod, struct kpatch_func *funcs,
 	}
 
 	/* Register the ftrace trampoline if it hasn't been done already. */
-	if (!kpatch_num_registered++) { /* TODO atomic */
+	if (!kpatch_num_registered++) {
 		ret = register_ftrace_function(&kpatch_ftrace_ops);
 		if (ret) {
 			printk("kpatch: can't register ftrace function \n");
@@ -252,6 +256,7 @@ int kpatch_register(struct module *mod, struct kpatch_func *funcs,
 	pr_notice("loaded patch module \"%s\"\n", mod->name);
 
 out:
+	up(&kpatch_mutex);
 	return ret;
 }
 EXPORT_SYMBOL(kpatch_register);
@@ -265,6 +270,8 @@ int kpatch_unregister(struct module *mod, struct kpatch_func *funcs,
 		.num_funcs = num_funcs,
 	};
 
+	down(&kpatch_mutex);
+
 	ret = stop_machine(kpatch_remove_patch, &args, NULL);
 	if (ret)
 		goto out;
@@ -293,6 +300,7 @@ int kpatch_unregister(struct module *mod, struct kpatch_func *funcs,
 	pr_notice("unloaded patch module \"%s\"\n", mod->name);
 
 out:
+	up(&kpatch_mutex);
 	return ret;
 }
 EXPORT_SYMBOL(kpatch_unregister);