Messages in this thread | | | Date | Thu, 16 Aug 2007 15:48:54 -0400 | From | Chris Snook <> | Subject | Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures |
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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.
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