Alex Ivchenko <aivchenko@ueidaq.com> writes:
> Hi,
>
> I tried to speed up a driver and moved copy_to_user()
> from ioctl to the bottom half of interrupt handler.
>
> access_ok() returns TRUE (of course, user address is valid), but
> copy_to_user() couldn't copy anything into the user space.
>
> bh is sched like:
> queue_task(&pd_bh_task, &tq_immediate);
> mark_bh(IMMEDIATE_BH);
>
> and spin_lock_irqsave() is NOT used in bh as well as any other
> sync stuff.
>
> I assumed that if lock is not set kernel could use exception handlers
> (according to Documentation/exception.txt) to get user space mem page.
>
> Could you tell me what is wrong?
You cannot do that. copy_*_user requires a process context, and
a bottom half does not have one (or at least not the one you want)
-Andi
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