diff options
| -rw-r--r-- | include/linux/rcu_segcblist.h | 7 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 38 |
2 files changed, 33 insertions, 12 deletions
diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h index 8afe886e85f1..3db96c4f45fd 100644 --- a/include/linux/rcu_segcblist.h +++ b/include/linux/rcu_segcblist.h @@ -109,7 +109,7 @@ struct rcu_cblist { * | SEGCBLIST_KTHREAD_GP | * | | * | Kthreads handle callbacks holding nocb_lock, local rcu_core() stops | - * | handling callbacks. | + * | handling callbacks. Enable bypass queueing. | * ---------------------------------------------------------------------------- */ @@ -125,7 +125,7 @@ struct rcu_cblist { * | SEGCBLIST_KTHREAD_GP | * | | * | CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core() | - * | ignores callbacks. | + * | ignores callbacks. Bypass enqueue is enabled. | * ---------------------------------------------------------------------------- * | * v @@ -134,7 +134,8 @@ struct rcu_cblist { * | SEGCBLIST_KTHREAD_GP | * | | * | CB/GP kthreads and local rcu_core() handle callbacks concurrently | - * | holding nocb_lock. Wake up CB and GP kthreads if necessary. | + * | holding nocb_lock. Wake up CB and GP kthreads if necessary. Disable | + * | bypass enqueue. | * ---------------------------------------------------------------------------- * | * v diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index e392bd129316..b08564b2bcf7 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1830,11 +1830,22 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, unsigned long j = jiffies; long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lockdep_assert_irqs_disabled(); + + // Pure softirq/rcuc based processing: no bypassing, no + // locking. if (!rcu_rdp_is_offloaded(rdp)) { *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + return false; + } + + // In the process of (de-)offloading: no bypassing, but + // locking. + if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { + rcu_nocb_lock(rdp); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); return false; /* Not offloaded, no bypassing. */ } - lockdep_assert_irqs_disabled(); // Don't use ->nocb_bypass during early boot. if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) { @@ -2416,7 +2427,16 @@ static long rcu_nocb_rdp_deoffload(void *arg) pr_info("De-offloading %d\n", rdp->cpu); rcu_nocb_lock_irqsave(rdp, flags); - + /* + * Flush once and for all now. This suffices because we are + * running on the target CPU holding ->nocb_lock (thus having + * interrupts disabled), and because rdp_offload_toggle() + * invokes rcu_segcblist_offload(), which clears SEGCBLIST_OFFLOADED. + * Thus future calls to rcu_segcblist_completely_offloaded() will + * return false, which means that future calls to rcu_nocb_try_bypass() + * will refuse to put anything into the bypass. + */ + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies)); ret = rdp_offload_toggle(rdp, false, flags); swait_event_exclusive(rdp->nocb_state_wq, !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB | @@ -2428,21 +2448,21 @@ static long rcu_nocb_rdp_deoffload(void *arg) del_timer_sync(&rdp->nocb_timer); /* - * Flush bypass. While IRQs are disabled and once we set - * SEGCBLIST_SOFTIRQ_ONLY, no callback is supposed to be - * enqueued on bypass. + * Theoretically we could set SEGCBLIST_SOFTIRQ_ONLY with CB unlocked + * and IRQs disabled but let's be paranoid. */ rcu_nocb_lock_irqsave(rdp, flags); - rcu_nocb_flush_bypass(rdp, NULL, jiffies); rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY); /* * With SEGCBLIST_SOFTIRQ_ONLY, we can't use - * rcu_nocb_unlock_irqrestore() anymore. Theoretically we - * could set SEGCBLIST_SOFTIRQ_ONLY with cb unlocked and IRQs - * disabled now, but let's be paranoid. + * rcu_nocb_unlock_irqrestore() anymore. */ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); + /* Sanity check */ + WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); + + return ret; } |