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Date: Tue, 17 Sep 2013 19:59:29 -0300
From: Lucas De Marchi <lucas.de.marchi@...il.com>
To: Rusty Russell <rusty@...tcorp.com.au>
Cc: Peter Chen <peter.chen@...escale.com>,
lkml <linux-kernel@...r.kernel.org>,
linux-modules <linux-modules@...r.kernel.org>
Subject: Re: [RFC PATCH 1/1] module: Make wait module's refcount to zero
procedure as async
On Mon, Sep 16, 2013 at 12:47 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Lucas De Marchi <lucas.de.marchi@...il.com> writes:
>> On Thu, Sep 12, 2013 at 9:30 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>> Peter Chen <peter.chen@...escale.com> writes:
>>>> 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.
>
> Cc: Lucas De Marchi <lucas.de.marchi@...il.com>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>
> 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@...el.com>
Lucas De Marchi
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