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rcu: Push lock release to rcu_start_gp()'s callers
If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a second step in this direction by moving the release of this lock to rcu_start_gp()'s callers. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -1487,16 +1487,14 @@ static int __noreturn rcu_gp_kthread(void *arg)
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/*
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* Start a new RCU grace period if warranted, re-initializing the hierarchy
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* in preparation for detecting the next grace period. The caller must hold
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* the root node's ->lock, which is released before return. Hard irqs must
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* be disabled.
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* the root node's ->lock and hard irqs must be disabled.
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*
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* Note that it is legal for a dying CPU (which is marked as offline) to
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* invoke this function. This can happen when the dying CPU reports its
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* quiescent state.
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*/
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static void
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rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
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__releases(rcu_get_root(rsp)->lock)
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rcu_start_gp(struct rcu_state *rsp)
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{
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struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
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struct rcu_node *rnp = rcu_get_root(rsp);
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@ -1510,15 +1508,13 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
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*/
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rcu_advance_cbs(rsp, rnp, rdp);
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if (!rsp->gp_kthread ||
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!cpu_needs_another_gp(rsp, rdp)) {
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if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
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/*
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* Either we have not yet spawned the grace-period
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* task, this CPU does not need another grace period,
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* or a grace period is already in progress.
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* Either way, don't start a new grace period.
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*/
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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return;
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}
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rsp->gp_flags = RCU_GP_FLAG_INIT;
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@ -1528,15 +1524,14 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
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/* Wake up rcu_gp_kthread() to start the grace period. */
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wake_up(&rsp->gp_wq);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}
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/*
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* Report a full set of quiescent states to the specified rcu_state
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* data structure. This involves cleaning up after the prior grace
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* period and letting rcu_start_gp() start up the next grace period
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* if one is needed. Note that the caller must hold rnp->lock, as
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* required by rcu_start_gp(), which will release it.
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* if one is needed. Note that the caller must hold rnp->lock, which
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* is released before return.
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*/
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static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
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__releases(rcu_get_root(rsp)->lock)
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@ -2134,7 +2129,8 @@ __rcu_process_callbacks(struct rcu_state *rsp)
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local_irq_save(flags);
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if (cpu_needs_another_gp(rsp, rdp)) {
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raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
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rcu_start_gp(rsp, flags); /* releases above lock */
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rcu_start_gp(rsp);
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raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
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} else {
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local_irq_restore(flags);
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}
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@ -2214,11 +2210,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
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/* Start a new grace period if one not already started. */
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if (!rcu_gp_in_progress(rsp)) {
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unsigned long nestflag;
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struct rcu_node *rnp_root = rcu_get_root(rsp);
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raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
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rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
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raw_spin_lock(&rnp_root->lock);
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rcu_start_gp(rsp);
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raw_spin_unlock(&rnp_root->lock);
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} else {
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/* Give the grace period a kick. */
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rdp->blimit = LONG_MAX;
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@ -2174,7 +2174,6 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
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unsigned long c;
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bool d;
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unsigned long flags;
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unsigned long flags1;
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struct rcu_node *rnp = rdp->mynode;
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struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
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@ -2236,8 +2235,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
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c, rnp->level,
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rnp->grplo, rnp->grphi,
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"Startedroot");
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local_save_flags(flags1);
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rcu_start_gp(rdp->rsp, flags1); /* Rlses ->lock. */
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rcu_start_gp(rdp->rsp);
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raw_spin_unlock(&rnp->lock);
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}
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/* Clean up locking and irq state. */
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