[RFC PATCH 1/9] livepatch: simplify disable error path

Josh Poimboeuf
2015-02-09T17:31:31Z

If registering the function with ftrace has previously succeeded,
unregistering will almost never fail. Even if it does, it's not a fatal
error. We can still carry on and disable the klp_func from being used
by removing it from the klp_ops func stack.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
kernel/livepatch/core.c | 67 +++++++++++++------------------------------------
1 file changed, 17 insertions(+), 50 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 9adf86b..081df77 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -322,32 +322,20 @@ static void notrace klp_ftrace_handler(unsigned long ip,
klp_arch_set_pc(regs, (unsigned long)func->new_func);
}

-static int klp_disable_func(struct klp_func *func)
+static void klp_disable_func(struct klp_func *func)
{
struct klp_ops *ops;
- int ret;
-
- if (WARN_ON(func->state != KLP_ENABLED))
- return -EINVAL;

- if (WARN_ON(!func->old_addr))
- return -EINVAL;
+ WARN_ON(func->state != KLP_ENABLED);
+ WARN_ON(!func->old_addr);

ops = klp_find_ops(func->old_addr);
if (WARN_ON(!ops))
- return -EINVAL;
+ return;

if (list_is_singular(&ops->func_stack)) {
- ret = unregister_ftrace_function(&ops->fops);
- if (ret) {
- pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
- func->old_name, ret);
- return ret;
- }
-
- ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
- if (ret)
- pr_warn("function unregister succeeded but failed to clear the filter\n");
+ WARN_ON(unregister_ftrace_function(&ops->fops));
+ WARN_ON(ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0));

list_del_rcu(&func->stack_node);
list_del(&ops->node);
@@ -357,8 +345,6 @@ static int klp_disable_func(struct klp_func *func)
}

func->state = KLP_DISABLED;
-
- return 0;
}

static int klp_enable_func(struct klp_func *func)
@@ -419,23 +405,15 @@ err:
return ret;
}

-static int klp_disable_object(struct klp_object *obj)
+static void klp_disable_object(struct klp_object *obj)
{
struct klp_func *func;
- int ret;

- for (func = obj->funcs; func->old_name; func++) {
- if (func->state != KLP_ENABLED)
- continue;
-
- ret = klp_disable_func(func);
- if (ret)
- return ret;
- }
+ for (func = obj->funcs; func->old_name; func++)
+ if (func->state == KLP_ENABLED)
+ klp_disable_func(func);

obj->state = KLP_DISABLED;
-
- return 0;
}

static int klp_enable_object(struct klp_object *obj)
@@ -451,22 +429,19 @@ static int klp_enable_object(struct klp_object *obj)

for (func = obj->funcs; func->old_name; func++) {
ret = klp_enable_func(func);
- if (ret)
- goto unregister;
+ if (ret) {
+ klp_disable_object(obj);
+ return ret;
+ }
}
obj->state = KLP_ENABLED;

return 0;
-
-unregister:
- WARN_ON(klp_disable_object(obj));
- return ret;
}

static int __klp_disable_patch(struct klp_patch *patch)
{
struct klp_object *obj;
- int ret;

/* enforce stacking: only the last enabled patch can be disabled */
if (!list_is_last(&patch->list, &klp_patches) &&
@@ -476,12 +451,8 @@ static int __klp_disable_patch(struct klp_patch *patch)
pr_notice("disabling patch '%s'\n", patch->mod->name);

for (obj = patch->objs; obj->funcs; obj++) {
- if (obj->state != KLP_ENABLED)
- continue;
-
- ret = klp_disable_object(obj);
- if (ret)
- return ret;
+ if (obj->state == KLP_ENABLED)
+ klp_disable_object(obj);
}

patch->state = KLP_DISABLED;
@@ -931,7 +902,6 @@ static void klp_module_notify_going(struct klp_patch *patch,
{
struct module *pmod = patch->mod;
struct module *mod = obj->mod;
- int ret;

if (patch->state == KLP_DISABLED)
goto disabled;
@@ -939,10 +909,7 @@ static void klp_module_notify_going(struct klp_patch *patch,
pr_notice("reverting patch '%s' on unloading module '%s'\n",
pmod->name, mod->name);

- ret = klp_disable_object(obj);
- if (ret)
- pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
- pmod->name, mod->name, ret);
+ klp_disable_object(obj);

disabled:
klp_free_object_loaded(obj);
--
2.1.0