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 :-( Thanks, NeilBrown > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 45dfdcaee39bf6dd1785253c78e4805122ee8d93 > Author: Paul E. McKenney <paul...@linux.vnet.ibm.com> > 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 <ne...@suse.com> Signed-off-by: Paul > E. McKenney <paul...@linux.vnet.ibm.com> [ paulmck: Apply neilb > feedback on naming. ] > > 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; > }
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