On Wed, 2012-02-01 at 09:29 -0800, Linus Torvalds wrote: > On Wed, Feb 1, 2012 at 9:08 AM, Torvald Riegel <trie...@redhat.com> wrote: > > > > What do the kernel folks think about the C11 memory model? If you can > > spot any issues in there, the GCC community would certainly like to > > know. > > I don't think this is about memory models except very tangentially. > > Gcc currently accesses fields in a way that affects *independent* > fields, without checking their memory models at all. > > Even original C already has one memory model: "volatile" data is seen > outside the virtual C machine. And Jiri reports that even that > *original* memory model is being violated. We're taling about the one > from about 40 years ago.
For volatile, I agree. However, the original btrfs example was *without* a volatile, and that's why I raised the memory model point. This triggered an error in a concurrent execution, so that's memory model land, at least in C language standard. The example was a granularity-of-access violation, I agree. Nonetheless, C11 has rules for that, they have been written down, it would good to know whether these rules are sufficient for you. > We do end up doing > much more aggressive threading, with models that C11 simply doesn't > cover. Any specific examples for that would be interesting.
