diff options
| -rw-r--r-- | kernel/rcutree.c | 71 |
1 files changed, 51 insertions, 20 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e75df0c93ab..e234eb92a17 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -842,28 +842,24 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) struct rcu_node *rnp = rcu_get_root(rsp); if (!rcu_scheduler_fully_active || - !cpu_needs_another_gp(rsp, rdp) || - rsp->fqs_active) { - if (rcu_scheduler_fully_active && - cpu_needs_another_gp(rsp, rdp)) - rsp->fqs_need_gp = 1; - if (rnp->completed == rsp->completed) { - raw_spin_unlock_irqrestore(&rnp->lock, flags); - return; - } - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + !cpu_needs_another_gp(rsp, rdp)) { + /* + * Either the scheduler hasn't yet spawned the first + * non-idle task or this CPU does not need another + * grace period. Either way, don't start a new grace + * period. + */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + if (rsp->fqs_active) { /* - * Propagate new ->completed value to rcu_node structures - * so that other CPUs don't have to wait until the start - * of the next grace period to process their callbacks. + * This CPU needs a grace period, but force_quiescent_state() + * is running. Tell it to start one on this CPU's behalf. */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - rnp->completed = rsp->completed; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - } - local_irq_restore(flags); + rsp->fqs_need_gp = 1; + raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } @@ -947,6 +943,8 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { unsigned long gp_duration; + struct rcu_node *rnp = rcu_get_root(rsp); + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); @@ -958,7 +956,40 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) gp_duration = jiffies - rsp->gp_start; if (gp_duration > rsp->gp_max) rsp->gp_max = gp_duration; - rsp->completed = rsp->gpnum; + + /* + * We know the grace period is complete, but to everyone else + * it appears to still be ongoing. But it is also the case + * that to everyone else it looks like there is nothing that + * they can do to advance the grace period. It is therefore + * safe for us to drop the lock in order to mark the grace + * period as completed in all of the rcu_node structures. + * + * But if this CPU needs another grace period, it will take + * care of this while initializing the next grace period. + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL + * because the callbacks have not yet been advanced: Those + * callbacks are waiting on the grace period that just now + * completed. + */ + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + + /* + * Propagate new ->completed value to rcu_node structures + * so that other CPUs don't have to wait until the start + * of the next grace period to process their callbacks. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + rnp->completed = rsp->gpnum; + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + } + rnp = rcu_get_root(rsp); + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + } + + rsp->completed = rsp->gpnum; /* Declare the grace period complete. */ trace_rcu_grace_period(rsp->name, rsp->completed, "end"); rsp->signaled = RCU_GP_IDLE; rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ |