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    SubjectRe: use of preempt_count instead of in_atomic() at leds-gpio.c
    On Fri, 21 Mar 2008, Andrew Morton wrote:

    > On Fri, 21 Mar 2008 10:53:11 +0100 Jean Delvare <khali@linux-fr.org> wrote:
    >
    > > On Thu, 20 Mar 2008 20:17:23 -0700, Andrew Morton wrote:
    > > > in_atomic() is for core kernel use only. (...)
    > >
    > > Then why is it made available to drivers through <linux/hardirq.h>?
    >
    > Because we suck.
    >
    > > If
    > > it's such a dangerous macro to call from drivers, it shouldn't be made
    > > available, or at the very least there should be a big fat warning in
    > > <linux/hardirq.h> that drivers aren't supposed to use it. This would
    > > have avoided the 23 uses cases in drivers we have right now.
    >
    > True.

    There's also a section about in_atomic() in the Linux Device Drivers
    (3rd ed.) book which may have contributed to the confusion. On p. 198:

    A function related to in_interrupt() is in_atomic(). Its
    return value is nonzero whenever scheduling is not allowed;
    this includes hardware and software interrupt contexts as well
    as any time when a spinlock is held. In the latter case,
    current may be valid, but access to user space is forbidden,
    since it can cause scheduling to happen. Whenever you are
    using in_interrupt(), you should really consider whether
    in_atomic() is what you actually mean. Both functions are
    declared in <asm/hardirq.h>.

    Alan Stern



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