[RFC PATCH 1/1] module: Make wait module's refcount to zero procedure as async

[Lucas De Marchi]

Currently, if module's refcount is not zero during the unload,
it waits there until the user decreases that refcount.

Hi Peter,
In practice userspace uses O_NONBLOCK. In fact, I've been
thinking of removing the blocking case altogether, since it's not really
what people want.
That would solve your problem and make the code simpler. Thoughts?

I'm all in favor of this. It's been almost 1 year it's deprecated in
kmod and if anyone tries to use we force a 10s delay on module
removal. So far nobody complained.
Lucas De Marchi

Here's what I've got in my pending-rebases tree.
Cheers,
Rusty.
module: remove rmmod --wait option.
The option to wait for a module reference count to reach zero was in
the initial module implementation, but it was never supported in
modprobe (you had to use rmmod --wait). After discussion with Lucas,
It has been deprecated (with a 10 second sleep) in kmod for the last
year.
This finally removes it: the flag will evoke a printk warning and a
normal (non-blocking) remove attempt.
diff --git a/include/linux/module.h b/include/linux/module.h
index 05f2447..15cd6b1 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -367,9 +367,6 @@ struct module
/* What modules do I depend on? */
struct list_head target_list;
- /* Who is waiting for us to be unloaded */
- struct task_struct *waiter;
-
/* Destruction function. */
void (*exit)(void);
diff --git a/kernel/module.c b/kernel/module.c
index dc58274..947105f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -644,8 +644,6 @@ static int module_unload_init(struct module *mod)
/* Hold reference count during initialization. */
__this_cpu_write(mod->refptr->incs, 1);
- /* Backwards compatibility macros put refcount during init. */
- mod->waiter = current;
return 0;
}
@@ -771,16 +769,9 @@ static int __try_stop_module(void *_sref)
static int try_stop_module(struct module *mod, int flags, int *forced)
{
- if (flags & O_NONBLOCK) {
- struct stopref sref = { mod, flags, forced };
+ struct stopref sref = { mod, flags, forced };
- return stop_machine(__try_stop_module, &sref, NULL);
- } else {
- /* We don't need to stop the machine for this. */
- mod->state = MODULE_STATE_GOING;
- synchronize_sched();
- return 0;
- }
+ return stop_machine(__try_stop_module, &sref, NULL);
}
unsigned long module_refcount(struct module *mod)
@@ -813,21 +804,6 @@ EXPORT_SYMBOL(module_refcount);
/* This exists whether we can unload or not */
static void free_module(struct module *mod);
-static void wait_for_zero_refcount(struct module *mod)
-{
- /* Since we might sleep for some time, release the mutex first */
- mutex_unlock(&module_mutex);
- for (;;) {
- pr_debug("Looking at refcount...\n");
- set_current_state(TASK_UNINTERRUPTIBLE);
- if (module_refcount(mod) == 0)
- break;
- schedule();
- }
- current->state = TASK_RUNNING;
- mutex_lock(&module_mutex);
-}
-
SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
unsigned int, flags)
{
@@ -842,6 +818,11 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
return -EFAULT;
name[MODULE_NAME_LEN-1] = '\0';
+ if (!(flags & O_NONBLOCK)) {
+ printk(KERN_WARNING
+ "waiting module removal not supported: please upgrade");
+ }
+
if (mutex_lock_interruptible(&module_mutex) != 0)
return -EINTR;
@@ -859,8 +840,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
/* Doing init or already dying? */
if (mod->state != MODULE_STATE_LIVE) {
- /* FIXME: if (force), slam module count and wake up
- waiter --RR */
+ /* FIXME: if (force), slam module count damn the torpedoes */
pr_debug("%s already dying\n", mod->name);
ret = -EBUSY;
goto out;
@@ -876,18 +856,11 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
}
}
- /* Set this up before setting mod->state */
- mod->waiter = current;
-
/* Stop the machine so refcounts can't move and disable module. */
ret = try_stop_module(mod, flags, &forced);
if (ret != 0)
goto out;
- /* Never wait if forced. */
- if (!forced && module_refcount(mod) != 0)
- wait_for_zero_refcount(mod);
-
mutex_unlock(&module_mutex);
/* Final destruction now no one is using it. */
if (mod->exit != NULL)
@@ -1005,9 +978,6 @@ void module_put(struct module *module)
__this_cpu_inc(module->refptr->decs);
trace_module_put(module, _RET_IP_);
- /* Maybe they're waiting for us to drop reference? */
- if (unlikely(!module_is_live(module)))
- wake_up_process(module->waiter);
preempt_enable();
}
}

Acked-by: Lucas De Marchi <lucas.demarchi-***@public.gmane.org>


Lucas De Marchi