On Wed, Aug 13, 2014 at 07:51:01PM +0200, Oleg Nesterov wrote:
> On 08/12, Luis R. Rodriguez wrote:
> >
> > +/* To be used by modules which can take over 30 seconds at probe */
>
> Probably the comment should explain that this hack should only be
> used if the driver is buggy and is wating for "real fix".
>
> > +#define module_long_probe_init(initfn) \
> > + static struct task_struct *__init_thread; \
> > + static int _long_probe_##initfn(void *arg) \
> > + { \
> > + return initfn(); \
> > + } \
> > + static inline __init int __long_probe_##initfn(void) \
> > + { \
> > + __init_thread = kthread_run(_long_probe_##initfn,\
> > + NULL, \
> > + #initfn); \
> > + if (IS_ERR(__init_thread)) \
> > + return PTR_ERR(__init_thread); \
> > + return 0; \
> > + } \
> > + module_init(__long_probe_##initfn);
> > +/* To be used by modules that require module_long_probe_init() */
> > +#define module_long_probe_exit(exitfn) \
> > + static inline void __long_probe_##exitfn(void) \
> > + { \
> > + exitfn(); \
> > + if (__init_thread) \
> > + kthread_stop(__init_thread); \
> > + } \
>
> exitfn() should be called after kthread_stop(), and only if initfn()
> returns 0. So it should probably do
>
> int err = kthread_stop(__init_thread);
> if (!err)
> exitfn();
Thanks! With the check for __init_thread as well as it can be
ERR_PTR(-ENOMEM), ERR_PTR(-EINTR), or NULL (for whatever other
reason).
> But there is an additional complication, you can't use __init_thread
> without get_task_struct(),
Can you elaborate why ? kthread_stop() uses get_task_struct(),
wake_up_process() and finally put_task_struct(), and we're the
only user of this thread. Also kthread_run() ensures wake_up_process()
gets called on startup, so not sure where the race would be provided
all users here and with the respective helpers on buggy drivers.
> so __long_probe_##initfn() can't use
> kthread_run(). It needs kthread_create() + get_task_struct() + wakeup.
I fail to see why we'd need to add get_task_struct() on
module_long_probe_init(), can you clarify?
Luis
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