On Tue, Jul 31, 2018 at 07:44:29AM -0700, Paul E. McKenney wrote: > On Tue, Jul 31, 2018 at 03:04:48PM +1000, NeilBrown wrote: > > On Mon, Jul 30 2018, Paul E. McKenney wrote: > > > > > On Tue, Jul 31, 2018 at 10:45:45AM +1000, NeilBrown wrote: > > >> On Fri, Jul 27 2018, Paul E. McKenney wrote: > > >> > > >> > On Thu, Jul 26, 2018 at 08:18:15PM -0700, Paul E. McKenney wrote: > > >> >> On Fri, Jul 27, 2018 at 11:04:37AM +1000, NeilBrown wrote: > > >> >> > On Wed, Jul 25 2018, Paul E. McKenney wrote: > > >> >> > >> > > >> >> > >> Looks good ... except ... naming is hard. > > >> >> > >> > > >> >> > >> is_after_call_rcu_init() asserts where in the lifecycle we are, > > >> >> > >> is_after_call_rcu() tests where in the lifecycle we are. > > >> >> > >> > > >> >> > >> The names are similar but the purpose is quite different. > > >> >> > >> Maybe s/is_after_call_rcu_init/call_rcu_init/ ?? > > >> >> > > > > >> >> > > How about rcu_head_init() and rcu_head_after_call_rcu()? > > >> >> > > >> >> Very well, I will pull this change in on my next rebase. > > >> > > > >> > Like this? > > >> > > >> Hard to say - unwinding white-space damage in my head is too challenging > > >> when newlines have been deleted :-( > > > > > > What??? Don't you like block-structured code? > > > > > > All kidding aside, how about the following more conventionally formatted > > > version? > > > > Wow - it's like I just got new glasses! > > Yes - nice an clear and now flaws to be found. Thanks a lot. > > Now that flaws are to be found, please feel free to report them. ;-) Hello, Neil, Any plans to use these functions? There are still no upstream uses. On the other hand, if they proved unuseful, I will remove them. If I don't hear otherwise from you, I will pull them in v5.2. Thanx, Paul > > NeilBrown > > > > > > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > commit e3408141ed7d702995b2fdc94703af88aadd226b > > > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > > Date: Tue Jul 24 15:28:09 2018 -0700 > > > > > > rcu: Provide functions for determining if call_rcu() has been invoked > > > > > > This commit adds rcu_head_init() and rcu_head_after_call_rcu() functions > > > to help RCU users detect when another CPU has passed the specified > > > rcu_head structure and function to call_rcu(). The rcu_head_init() > > > should be invoked before making the structure visible to RCU readers, > > > and then the rcu_head_after_call_rcu() may be invoked from within > > > an RCU read-side critical section on an rcu_head structure that > > > was obtained during a traversal of the data structure in question. > > > The rcu_head_after_call_rcu() function will return true if the rcu_head > > > structure has already been passed (with the specified function) to > > > call_rcu(), otherwise it will return false. > > > > > > If rcu_head_init() has not been invoked on the rcu_head structure > > > or if the rcu_head (AKA callback) has already been invoked, then > > > rcu_head_after_call_rcu() will do WARN_ON_ONCE(). > > > > > > Reported-by: NeilBrown <neilb@xxxxxxxx> > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > > [ paulmck: Apply neilb naming feedback. ] > > > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > index e4f821165d0b..4db8bcacc51a 100644 > > > --- a/include/linux/rcupdate.h > > > +++ b/include/linux/rcupdate.h > > > @@ -857,6 +857,46 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) > > > #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ > > > > > > > > > +/* Has the specified rcu_head structure been handed to call_rcu()? */ > > > + > > > +/* > > > + * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() > > > + * @rhp: The rcu_head structure to initialize. > > > + * > > > + * If you intend to invoke rcu_head_after_call_rcu() to test whether a > > > + * given rcu_head structure has already been passed to call_rcu(), then > > > + * you must also invoke this rcu_head_init() function on it just after > > > + * allocating that structure. Calls to this function must not race with > > > + * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. > > > + */ > > > +static inline void rcu_head_init(struct rcu_head *rhp) > > > +{ > > > + rhp->func = (rcu_callback_t)~0L; > > > +} > > > + > > > +/* > > > + * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()? > > > + * @rhp: The rcu_head structure to test. > > > + * @func: The function passed to call_rcu() along with @rhp. > > > + * > > > + * Returns @true if the @rhp has been passed to call_rcu() with @func, > > > + * and @false otherwise. Emits a warning in any other case, including > > > + * the case where @rhp has already been invoked after a grace period. > > > + * Calls to this function must not race with callback invocation. One way > > > + * to avoid such races is to enclose the call to rcu_head_after_call_rcu() > > > + * in an RCU read-side critical section that includes a read-side fetch > > > + * of the pointer to the structure containing @rhp. > > > + */ > > > +static inline bool > > > +rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) > > > +{ > > > + if (READ_ONCE(rhp->func) == f) > > > + return true; > > > + WARN_ON_ONCE(READ_ONCE(rhp->func) != (rcu_callback_t)~0L); > > > + return false; > > > +} > > > + > > > + > > > /* Transitional pre-consolidation compatibility definitions. */ > > > > > > static inline void synchronize_rcu_bh(void) > > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > > index 5dec94509a7e..4c56c1d98fb3 100644 > > > --- a/kernel/rcu/rcu.h > > > +++ b/kernel/rcu/rcu.h > > > @@ -224,6 +224,7 @@ void kfree(const void *); > > > */ > > > static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head) > > > { > > > + rcu_callback_t f; > > > unsigned long offset = (unsigned long)head->func; > > > > > > rcu_lock_acquire(&rcu_callback_map); > > > @@ -234,7 +235,9 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head) > > > return true; > > > } else { > > > RCU_TRACE(trace_rcu_invoke_callback(rn, head);) > > > - head->func(head); > > > + f = head->func; > > > + WRITE_ONCE(head->func, (rcu_callback_t)0L); > > > + f(head); > > > rcu_lock_release(&rcu_callback_map); > > > return false; > > > } > >