On Fri, Mar 20, 2020 at 10:59:55AM -0400, Alan Stern wrote: > On Fri, 20 Mar 2020, Joel Fernandes (Google) wrote: > > > This adds an example for the important RCU grace period guarantee, which > > shows an RCU reader can never span a grace period. > > > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > --- > > .../litmus-tests/RCU+sync+free.litmus | 40 +++++++++++++++++++ > > 1 file changed, 40 insertions(+) > > create mode 100644 tools/memory-model/litmus-tests/RCU+sync+free.litmus > > > > diff --git a/tools/memory-model/litmus-tests/RCU+sync+free.litmus b/tools/memory-model/litmus-tests/RCU+sync+free.litmus > > new file mode 100644 > > index 0000000000000..c4682502dd296 > > --- /dev/null > > +++ b/tools/memory-model/litmus-tests/RCU+sync+free.litmus > > @@ -0,0 +1,40 @@ > > +C RCU+sync+free > > + > > +(* > > + * Result: Never > > + * > > The following comment needs some rewriting. The grammar is somewhat > awkward and a very important "not" is missing. > > > + * This litmus test demonstrates that an RCU reader can never see a write after > > + * the grace period, if it saw writes that happen before the grace period. > > An RCU reader can never see a write that follows a grace period if it > did _not_ see writes that precede the grace period. Yes, you are right. I will change your wording to 'did not see *all* writes that precede'. > > This > > + * is a typical pattern of RCU usage, where the write before the grace period > > + * assigns a pointer, and the writes after destroy the object that the pointer > > + * points to. > > ... that the pointer used to point to. Will fix. > > + * > > + * This guarantee also implies, an RCU reader can never span a grace period and > > + * is an important RCU grace period memory ordering guarantee. > > Unnecessary comma, and it is not clear what "This" refers to. The > whole sentence should be phrased differently: > > This is one implication of the RCU grace-period guarantee, > which says (among other things) that an RCU reader cannot span > a grace period. Your wording is better, will use that. thanks, - Joel
