Re: modules: set mod->state to GOING before going notifiers are called

From: Jessica Yu
Date: Thu Mar 10 2016 - 00:08:44 EST

+++ Rusty Russell [10/03/16 13:57 +1030]:
Jessica Yu <jeyu@xxxxxxxxxx> writes:
In load_module(), the going notifiers are called during error handling
when an error occurs after the coming notifiers have already been called.
However, a module's state is still MODULE_STATE_COMING when the going
notifiers are called in the error path. To be consistent, also set
mod->state to MODULE_STATE_GOING before calling the going notifiers.

Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
kernel/module.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index 1981ae0..9e80576 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3494,6 +3494,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
return do_init_module(mod);

+ mutex_lock(&module_mutex);
+ mod->state = MODULE_STATE_GOING;
+ mutex_unlock(&module_mutex);

Actually, reviewing this patch makes me realize it is wrong.

We rely on the state of the module being MODULE_STATE_COMING here:

static inline int strong_try_module_get(struct module *mod)
BUG_ON(mod && mod->state == MODULE_STATE_UNFORMED);
if (mod && mod->state == MODULE_STATE_COMING)
return -EBUSY;

We will just have to document that the notifier can be called with
a module in MODULE_STATE_COMING if it never succeeded its

Ah, thanks for catching that. I think I remember seeing this conditional and
assuming it wouldn't be a problem since GOING modules would fail in
try_module_get() (as it is does not pass the module_is_live() test) and
subsequently strong_try_module_get() would also fail.. But, I think I ought to
review how module states interact before making a change like this, so, please
ignore this patch.