Re: [patch 6/11] s390: in_interrupt vs. in_atomic.

[Martin Schwidefsky]

> > The condition for no context in do_exception checks for hard and
> > soft interrupts by using in_interrupt() but not for preemption.
> > This is bad for the users of __copy_from/to_user_inatomic because
> > the fault handler might call schedule although the preemption
> > count is != 0. Use in_atomic() instead in_interrupt().
> >
>
> hm.  Under what circumstances do you expect this test to trigger?

e.g. by the following:

static inline int get_futex_value_locked(int *dest, int __user *from)
{
        int ret;

        inc_preempt_count();
        ret = __copy_from_user_inatomic(dest, from, sizeof(int));
        dec_preempt_count();
        preempt_check_resched();

        return ret ? -EFAULT : 0;
}

in_interrupt only checks for HARDIRQ_MASK and SOFTIRQ_MASK but not
for the preemption counter. This is not a theory, we had a bug report
concerning a "bad: scheduling while atomic!" warning.

blue skies,
   Martin

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH


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