Damn, sorry for noise ;)
I was going to suggest to introduce module_put_and_exit() to simplify
this and potentially other users, but it already exists. So this code
can use it too without additional complications.
On 08/17, Oleg Nesterov wrote:
> On 08/17, Oleg Nesterov wrote:
> >
> > On 08/17, Takashi Iwai wrote:
> > >
> > > How about just increasing/decreasing the module count for blocking the
> > > exit call? For example:
> > >
> > > #define module_long_probe_init(initfn) \
> > > static int _long_probe_##initfn(void *arg) \
> > > { \
> > > int ret = initfn(); \
> > > module_put(THIS_MODULE); \
> >
> > WINDOW, please see below.
> >
> > > return ret; \
> > > } \
> > > static inline __init int __long_probe_##initfn(void) \
> > > { \
> > > struct task_struct *__init_thread; \
> > > __module_get(THIS_MODULE); \
> > > __init_thread = kthread_run(_long_probe_##initfn,\
> > > NULL, \
> > > #initfn); \
> > > if (IS_ERR(__init_thread)) { \
> > > module_put(THIS_MODULE); \
> > > return PTR_ERR(__init_thread); \
> > > } \
> > > return 0; \
> > > } \
> >
> > I leave this to you and Luis, but personally I think this is very
> > nice idea, I like it. Because sys_delete_module() won't hang in D
> > state waiting for initfn().
> >
> > There is a small problem. This module can be unloaded right after
> > module_put() above. In this case its memory can be unmapped and
> > the exiting thread can crash.
> >
> > This is very unlikely, this thread needs to execute just a few insn
> > and escape from this module's memory. Given that only the buggy
> > modules should use this hack, perhaps we can even ignore this race.
> >
> > But perhaps it makes sense to close this race anyway, and we already
> > have complete_and_exit() which can be used instead of "return ret"
> > above. Just we need the additional "static struct completion" and
> > module_exit() should call wait_for_completion.
>
> Forgot to mention... and __long_probe_##initfn() could be simpler
> without kthread_run,
>
> __init_thread = kthread_create(...);
> if (IS_ERR(__init_thread))
> return PTR_ERR();
>
> module_get(THIS_MODULE);
> wake_up_process(__init_thread);
> return 0;
>
> but this is subjective, up to you.
>
> Oleg.
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