On Tue, Nov 27, 2018 at 01:26:42AM +0100, Andrea Parri wrote: > > commit 72f61917f12236514a70017d1ebafb9b8d34a9b6 > > Author: Paul E. McKenney <paul...@linux.ibm.com> > > Date: Mon Nov 26 14:26:43 2018 -0800 > > > > tools/memory-model: Update README for addition of SRCU > > > > This commit updates the section on LKMM limitations to no longer say > > that SRCU is not modeled, but instead describe how LKMM's modeling of > > SRCU departs from the Linux-kernel implementation. > > > > TL;DR: There is no known valid use case that cares about the Linux > > kernel's ability to have partially overlapping SRCU read-side critical > > sections. > > > > Signed-off-by: Paul E. McKenney <paul...@linux.ibm.com> > > Indeed!, > > Acked-by: Andrea Parri <andrea.pa...@amarulasolutions.com>
Thank you, applied! I moved this commit and Alan's three SRCU commits to the branch destined for the upcoming merge window. Thanx, Paul > Andrea > > > > > > diff --git a/tools/memory-model/README b/tools/memory-model/README > > index 0f2c366518c6..9d7d4f23503f 100644 > > --- a/tools/memory-model/README > > +++ b/tools/memory-model/README > > @@ -221,8 +221,29 @@ The Linux-kernel memory model has the following > > limitations: > > additional call_rcu() process to the site of the > > emulated rcu-barrier(). > > > > - e. Sleepable RCU (SRCU) is not modeled. It can be > > - emulated, but perhaps not simply. > > + e. Although sleepable RCU (SRCU) is now modeled, there > > + are some subtle differences between its semantics and > > + those in the Linux kernel. For example, the kernel > > + might interpret the following sequence as two partially > > + overlapping SRCU read-side critical sections: > > + > > + 1 r1 = srcu_read_lock(&my_srcu); > > + 2 do_something_1(); > > + 3 r2 = srcu_read_lock(&my_srcu); > > + 4 do_something_2(); > > + 5 srcu_read_unlock(&my_srcu, r1); > > + 6 do_something_3(); > > + 7 srcu_read_unlock(&my_srcu, r2); > > + > > + In contrast, LKMM will interpret this as a nested pair of > > + SRCU read-side critical sections, with the outer critical > > + section spanning lines 1-7 and the inner critical section > > + spanning lines 3-5. > > + > > + This difference would be more of a concern had anyone > > + identified a reasonable use case for partially overlapping > > + SRCU read-side critical sections. For more information, > > + please see: https://paulmck.livejournal.com/40593.html > > > > f. Reader-writer locking is not modeled. It can be > > emulated in litmus tests using atomic read-modify-write > > >