Re: use of preempt_count instead of in_atomic() at leds-gpio.c

[Stefan Richter]

PS,
I wrote:
> Tetsuo Handa wrote:
> > So, it is impossible to know whether I am inside a spinlock or not.
> > OK. That's not what I want to do.
> >
> > I want to make sure that my code (not a device driver) is called only 
> > from a context where use of down()/mutex_lock()/kmalloc(GFP_KERNEL)/
> > get_user_pages()/kmap() etc. are permitted.
> > Is "if (in_atomic()) return;" check a correct method for avoiding 
> > deadlocks when my code was accidentally called from a context
> > where use of down()/mutex_lock()/kmalloc(GFP_KERNEL)/get_user_pages()/
> > kmap() etc. are not permitted?

No.  Quoting Andrew:  "in_atomic() returns false inside spinlock on 
non-preemptible kernels."

> You shouldn't sleep while holding a spinlock.  As soon as another thread 

or interrupt handler or tasklet

> attempts to take the spinlock, it will be stuck in a busy-wait loop.
--
Stefan Richter
-=====-==--- --== =-=-=
http://arcgraph.de/sr/
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