Satyam Sharma wrote:
On Fri, 17 Aug 2007, Nick Piggin wrote:Satyam Sharma wrote: [...]Granted, the above IS buggy code. But, the stated objective is to avoid heisenbugs.^^^^^^^^^^Anyway, why are you making up code snippets that are buggy in other ways in order to support this assertion being made that lots of kernel code supposedly depends on volatile semantics. Just reference the actual code.Because the point is *not* about existing bugs in kernel code. At some point Chris Snook (who started this thread) did write that "If I knew of the existing bugs in the kernel, I would be sending patches for them, not this series" or something to that effect. The point is about *author expecations*. If people do expect atomic_read() (or a variant thereof) to have volatile semantics, why not give them such a variant?
Because they should be thinking about them in terms of barriers, over which the compiler / CPU is not to reorder accesses or cache memory operations, rather than "special" "volatile" accesses. Linux's whole memory ordering and locking model is completely geared around the former.
And by the way, the point is *also* about the fact that cpu_relax(), as of today, implies a full memory clobber, which is not what a lot of such loops want. (due to stuff mentioned elsewhere, summarized in that summary)
That's not the point, because as I also mentioned, the logical extention to Linux's barrier API to handle this is the order(x) macro. Again, not special volatile accessors. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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