On Thu, 15 Nov 2018, Paul E. McKenney wrote: > On Thu, Nov 15, 2018 at 11:19:24AM -0500, Alan Stern wrote: > > Paul and other LKMM maintainers: > > > > The following series of patches adds support for SRCU to the Linux > > Kernel Memory Model. That is, it adds the srcu_read_lock(), > > srcu_read_unlock(), and synchronize_srcu() primitives to the model. > > > > Patch 1/3 does some renaming of the RCU parts of the > > memory model's existing CAT code, to help distinguish them > > from the upcoming SRCU parts. > > > > Patch 2/3 refactors the definitions of some RCU relations > > in the CAT code, in a way that the SRCU portions will need. > > > > Patch 3/3 actually adds the SRCU support. > > > > This new code requires herd7 version 7.51+4(dev) or later (now > > available in the herdtools7 github repository) to run. Thanks to Luc > > for making the necessary changes to support SRCU. > > These patches pass the tests that I have constructed, and also regression > tests, very nice! Applied and pushed, thank you. > > > The code does not check that the index argument passed to > > srcu_read_unlock() is the same as the value returned by the > > corresponding srcu_read_lock() call. This is deemed to be a semantic > > issue, not directly relevant to the memory model. > > Agreed. > > If I understand correctly, there are in theory some use cases that these > patches do not support, for example: > > r1 = srcu_read_lock(a); > do_1(); > r2 = srcu_read_lock(a); > do_2(); > srcu_read_unlock(a, r1); > do_3(); > srcu_read_unlock(a, r2);
Yes, this sort of thing will be misinterpreted as two nested critical sections rather than two overlapping critical sections. > In practice, I would be more worried about this had I ever managed to > find a non-bogus use case for this pattern. ;-) The example is also a little difficult for humans to follow, at least without an explanatory comment. Alan
