Messages in this thread | | | Date | Tue, 27 Nov 2018 01:26:42 +0100 | From | Andrea Parri <> | Subject | Re: [PATCH 0/3] tools/memory-model: Add SRCU support |
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> commit 72f61917f12236514a70017d1ebafb9b8d34a9b6 > Author: Paul E. McKenney <paulmck@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 <paulmck@linux.ibm.com>
Indeed!,
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
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 >
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