On Mon, Apr 17, 2017 at 05:33:32PM -0700, Josh Triplett wrote: > On Mon, Apr 17, 2017 at 04:44:51PM -0700, Paul E. McKenney wrote: > > Users of SRCU are obliged to complete all grace-period activity before > > invoking cleanup_srcu_struct(). This means that all calls to either > > synchronize_srcu() or synchronize_srcu_expedited() must have returned, > > and all calls to call_srcu() must have returned, and the last call to > > call_srcu() must have been followed by a call to srcu_barrier(). > > Furthermore, the caller must have done something to prevent any > > further calls to synchronize_srcu(), synchronize_srcu_expedited(), > > and call_srcu(). > > > > Therefore, if there has ever been an invocation of call_srcu() on > > the srcu_struct in question, the sequence of events must be as > > follows: > > > > 1. Prevent any further calls to call_srcu(). > > 2. Wait for any pre-existing call_srcu() invocations to return. > > 3. Invoke srcu_barrier(). > > 4. It is now safe to invoke cleanup_srcu_struct(). > > > > On the other hand, if there has ever been a call to synchronize_srcu() > > or synchronize_srcu_expedited(), the sequence of events must be as > > follows: > > > > 1. Prevent any further calls to synchronize_srcu() or > > synchronize_srcu_expedited(). > > 2. Wait for any pre-existing synchronize_srcu() or > > synchronize_srcu_expedited() invocations to return. > > 3. It is now safe to invoke cleanup_srcu_struct(). > > > > If there have been calls to all both types of functions (call_srcu() > > and either of synchronize_srcu() and synchronize_srcu_expedited()), then > > the caller must do the first three steps of the call_srcu() procedure > > above and the first two steps of the synchronize_s*() procedure above, > > and only then invoke cleanup_srcu_struct(). > > This commit message clearly explains the correct sequence for the > client, but not which aspects of this the change now enforces. Some of > the steps above remain the responsibility of the caller, while the > callee now checks more of them. Could you add something at the end > explaining the change and what it enforces?
More importantly, perhaps this explanation could find its way into the documentation of cleanup_srcu_struct? > > Reported-by: Paolo Bonzini <[email protected]> > > Signed-off-by: Paul E. McKenney <[email protected]> > > With the above change: > Reviewed-by: Josh Triplett <[email protected]> > > > kernel/rcu/srcu.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c > > index ba41a5d04b49..6beeba7b0b67 100644 > > --- a/kernel/rcu/srcu.c > > +++ b/kernel/rcu/srcu.c > > @@ -261,6 +261,11 @@ void cleanup_srcu_struct(struct srcu_struct *sp) > > { > > if (WARN_ON(srcu_readers_active(sp))) > > return; /* Leakage unless caller handles error. */ > > + if (WARN_ON(!rcu_all_batches_empty(sp))) > > + return; /* Leakage unless caller handles error. */ > > + flush_delayed_work(&sp->work); > > + if (WARN_ON(sp->running)) > > + return; /* Caller forgot to stop doing call_srcu()? */ > > free_percpu(sp->per_cpu_ref); > > sp->per_cpu_ref = NULL; > > } > > -- > > 2.5.2 > >
