linux-kernel - Re: use of preempt_count instead of in

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Date:	Sat, 22 Mar 2008 00:11:40 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: use of preempt_count instead of in_atomic() at leds-gpio.c

Hello.

> > In short, you are saying that there is _no_ reliable way to determine
> > am-i-called-from-inside-spinlock.
> 
> That's correct.

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?
I'm assuming that in_atomic() returns nonzero whenever scheduling is not permitted.

Regards.
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