From 1217ed1ba5c67393293dfb0f03c353b118dadeb4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 4 May 2011 21:43:49 -0700 Subject: rcu: permit rcu_read_unlock() to be called while holding runqueue locks Avoid calling into the scheduler while holding core RCU locks. This allows rcu_read_unlock() to be called while holding the runqueue locks, but only as long as there was no chance of the RCU read-side critical section having been preempted. (Otherwise, if RCU priority boosting is enabled, rcu_read_unlock() might call into the scheduler in order to unboost itself, which might allows self-deadlock on the runqueue locks within the scheduler.) Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 44 +++++++++++++------------------------------- 1 file changed, 13 insertions(+), 31 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 54ff7eb..5616b17 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1133,22 +1133,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) raw_spin_unlock_irqrestore(&rnp->lock, flags); if (need_report & RCU_OFL_TASKS_EXP_GP) rcu_report_exp_rnp(rsp, rnp); - - /* - * If there are no more online CPUs for this rcu_node structure, - * kill the rcu_node structure's kthread. Otherwise, adjust its - * affinity. - */ - t = rnp->node_kthread_task; - if (t != NULL && - rnp->qsmaskinit == 0) { - raw_spin_lock_irqsave(&rnp->lock, flags); - rnp->node_kthread_task = NULL; - raw_spin_unlock_irqrestore(&rnp->lock, flags); - kthread_stop(t); - rcu_stop_boost_kthread(rnp); - } else - rcu_node_kthread_setaffinity(rnp, -1); + rcu_node_kthread_setaffinity(rnp, -1); } /* @@ -1320,8 +1305,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) return; } if (rnp->qsmask == 0) { - rcu_initiate_boost(rnp); - raw_spin_unlock_irqrestore(&rnp->lock, flags); + rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ continue; } cpu = rnp->grplo; @@ -1340,10 +1324,10 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) raw_spin_unlock_irqrestore(&rnp->lock, flags); } rnp = rcu_get_root(rsp); - raw_spin_lock_irqsave(&rnp->lock, flags); - if (rnp->qsmask == 0) - rcu_initiate_boost(rnp); - raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (rnp->qsmask == 0) { + raw_spin_lock_irqsave(&rnp->lock, flags); + rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ + } } /* @@ -1497,7 +1481,8 @@ static void invoke_rcu_cpu_kthread(void) /* * Wake up the specified per-rcu_node-structure kthread. - * The caller must hold ->lock. + * Because the per-rcu_node kthreads are immortal, we don't need + * to do anything to keep them alive. */ static void invoke_rcu_node_kthread(struct rcu_node *rnp) { @@ -1546,8 +1531,8 @@ static void rcu_cpu_kthread_timer(unsigned long arg) raw_spin_lock_irqsave(&rnp->lock, flags); rnp->wakemask |= rdp->grpmask; - invoke_rcu_node_kthread(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); + invoke_rcu_node_kthread(rnp); } /* @@ -1694,16 +1679,12 @@ static int rcu_node_kthread(void *arg) for (;;) { rnp->node_kthread_status = RCU_KTHREAD_WAITING; - wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 || - kthread_should_stop()); - if (kthread_should_stop()) - break; + wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0); rnp->node_kthread_status = RCU_KTHREAD_RUNNING; raw_spin_lock_irqsave(&rnp->lock, flags); mask = rnp->wakemask; rnp->wakemask = 0; - rcu_initiate_boost(rnp); - raw_spin_unlock_irqrestore(&rnp->lock, flags); + rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { if ((mask & 0x1) == 0) continue; @@ -1719,6 +1700,7 @@ static int rcu_node_kthread(void *arg) preempt_enable(); } } + /* NOTREACHED */ rnp->node_kthread_status = RCU_KTHREAD_STOPPED; return 0; } @@ -1738,7 +1720,7 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) int cpu; unsigned long mask = rnp->qsmaskinit; - if (rnp->node_kthread_task == NULL || mask == 0) + if (rnp->node_kthread_task == NULL) return; if (!alloc_cpumask_var(&cm, GFP_KERNEL)) return; -- cgit v1.1