Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

Herbert Xu wrote:

On Thu, Aug 16, 2007 at 10:06:31AM +0200, Stefan Richter wrote:

Do you (or anyone else for that matter) have an example of this?

The only code I somewhat know, the ieee1394 subsystem, was perhaps
authored and is currently maintained with the expectation that each
occurrence of atomic_read actually results in a load operation, i.e. is
not optimized away.  This means all atomic_t (bus generation, packet and
buffer refcounts, and some other state variables)* and likewise all
atomic bitops in that subsystem.

Can you find an actual atomic_read code snippet there that is
broken without the volatile modifier?

A whole bunch of atomic_read uses will be broken without the volatile modifier once we start removing barriers that aren't needed if volatile behavior is guaranteed.

barrier() clobbers all your registers. volatile atomic_read() only clobbers one register, and more often than not it's a register you wanted to clobber anyway.

	-- Chris
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