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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