Re: [patch] Re: using long instead of atomic_t when only set/readis required

[Alan Stern]

On Mon, 3 Mar 2008, Alan Cox wrote:

> > Atomicity of reads of write for pointers and integral types (other than 
> > long long) should be documented.
> 
> NAK.
> 
> Atomicity of reads or writes for pointers and integral types is NOT
> guaranteed. Gcc doesn't believe in your guarantee.

Miscommunication and lack of clarity.  CPU reads and writes _are_ 
guaranteed to be atomic.  What is not guaranteed is that the compiler 
will generate a single read or write instruction corresponding to a 
particular expression in C.

Consider a routine like the following:

	static task_struct *the_task;

	void store_task(void)
	{
		the_task = current;
	}

Is it possible to say whether readers examining "the_task" are 
guaranteed to see a coherent value?

Alan Stern		

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