Re: use of preempt_count instead of in_atomic() at leds-gpio.c
[Posted March 24, 2008 by corbet]
| From: |
| Alan Stern <stern-AT-rowland.harvard.edu> |
| To: |
| Andrew Morton <akpm-AT-linux-foundation.org> |
| Subject: |
| Re: use of preempt_count instead of in_atomic() at leds-gpio.c |
| Date: |
| Fri, 21 Mar 2008 14:05:59 -0400 (EDT) |
| Message-ID: |
| <Pine.LNX.4.44L0.0803211343240.24421-100000@netrider.rowland.org> |
| Cc: |
| Jean Delvare <khali-AT-linux-fr.org>, Michael Buesch <mb-AT-bu3sch.de>,
Henrique de Moraes Holschuh <hmh-AT-hmh.eng.br>,
David Brownell <david-b-AT-pacbell.net>,
Richard Purdie <rpurdie-AT-rpsys.net>,
Kernel development list <linux-kernel-AT-vger.kernel.org>,
Ingo Molnar <mingo-AT-elte.hu>,
Geert Uytterhoeven <geert-AT-linux-m68k.org>,
Jonathan Corbet <corbet-AT-lwn.net> |
| Archive‑link: | |
Article |
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