On Fri, Nov 06, 2020 at 10:01:02AM -0800, Paul E. McKenney wrote: > On Fri, Nov 06, 2020 at 09:47:22AM +0800, Boqun Feng wrote: > > On Thu, Nov 05, 2020 at 02:00:14PM -0800, paulmck@xxxxxxxxxx wrote: > > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > --- > > > tools/memory-model/Documentation/glossary.txt | 155 ++++++++++++++++++++++++++ > > > 1 file changed, 155 insertions(+) > > > create mode 100644 tools/memory-model/Documentation/glossary.txt > > > > > > diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt > > > new file mode 100644 > > > index 0000000..036fa28 > > > --- /dev/null > > > +++ b/tools/memory-model/Documentation/glossary.txt > > > @@ -0,0 +1,155 @@ > > > +This document contains brief definitions of LKMM-related terms. Like most > > > +glossaries, it is not intended to be read front to back (except perhaps > > > +as a way of confirming a diagnosis of OCD), but rather to be searched > > > +for specific terms. > > > + > > > + > > > +Address Dependency: When the address of a later memory access is computed > > > + based on the value returned by an earlier load, an "address > > > + dependency" extends from that load extending to the later access. > > > + Address dependencies are quite common in RCU read-side critical > > > + sections: > > > + > > > + 1 rcu_read_lock(); > > > + 2 p = rcu_dereference(gp); > > > + 3 do_something(p->a); > > > + 4 rcu_read_unlock(); > > > + > > > + In this case, because the address of "p->a" on line 3 is computed > > > + from the value returned by the rcu_dereference() on line 2, the > > > + address dependency extends from that rcu_dereference() to that > > > + "p->a". In rare cases, optimizing compilers can destroy address > > > + dependencies. Please see Documentation/RCU/rcu_dereference.txt > > > + for more information. > > > + > > > + See also "Control Dependency". > > > + > > > +Acquire: With respect to a lock, acquiring that lock, for example, > > > + using spin_lock(). With respect to a non-lock shared variable, > > > + a special operation that includes a load and which orders that > > > + load before later memory references running on that same CPU. > > > + An example special acquire operation is smp_load_acquire(), > > > + but atomic_read_acquire() and atomic_xchg_acquire() also include > > > + acquire loads. > > > + > > > + When an acquire load returns the value stored by a release store > > > + to that same variable, then all operations preceding that store > > > > Change this to: > > > > When an acquire load reads-from a release store > > > > , and put a reference to "Reads-from"? I think this makes the document > > more consistent in that it makes clear "an acquire load returns the > > value stored by a release store to the same variable" is not a special > > case, it's simple a "Reads-from". > > > > > + happen before any operations following that load acquire. > > > > Add a reference to the definition of "happen before" in explanation.txt? > > How about as shown below? I currently am carrying this as a separate > commit, but I might merge it into this one later on. > Looks good to me, thanks! Regards, Boqun > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 774a52cd3d80d6b657ae6c14c10bd9fc437068f3 > Author: Paul E. McKenney <paulmck@xxxxxxxxxx> > Date: Fri Nov 6 09:58:01 2020 -0800 > > tools/memory-model: Tie acquire loads to reads-from > > This commit explicitly makes the connection between acquire loads and > the reads-from relation. It also adds an entry for happens-before, > and refers to the corresponding section of explanation.txt. > > Reported-by: Boqun Feng <boqun.feng@xxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt > index 3924aca..383151b 100644 > --- a/tools/memory-model/Documentation/glossary.txt > +++ b/tools/memory-model/Documentation/glossary.txt > @@ -33,10 +33,11 @@ Acquire: With respect to a lock, acquiring that lock, for example, > acquire loads. > > When an acquire load returns the value stored by a release store > - to that same variable, then all operations preceding that store > - happen before any operations following that load acquire. > + to that same variable, (in other words, the acquire load "reads > + from" the release store), then all operations preceding that > + store "happen before" any operations following that load acquire. > > - See also "Relaxed" and "Release". > + See also "Happens-Before", "Reads-From", "Relaxed", and "Release". > > Coherence (co): When one CPU's store to a given variable overwrites > either the value from another CPU's store or some later value, > @@ -102,6 +103,11 @@ Fully Ordered: An operation such as smp_mb() that orders all of > that orders all of its CPU's prior accesses, itself, and > all of its CPU's subsequent accesses. > > +Happens-Before (hb): A relation between two accesses in which LKMM > + guarantees the first access precedes the second. For more > + detail, please see the "THE HAPPENS-BEFORE RELATION: hb" > + section of explanation.txt. > + > Marked Access: An access to a variable that uses an special function or > macro such as "r1 = READ_ONCE()" or "smp_store_release(&a, 1)". >
