diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcutree.c | 5 | ||||
| -rw-r--r-- | kernel/rcutree.h | 21 | ||||
| -rw-r--r-- | kernel/rcutree_plugin.h | 163 | ||||
| -rw-r--r-- | kernel/rcutree_trace.c | 11 |
4 files changed, 117 insertions, 83 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 90104a19c56..0ac1cc03f93 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1901,10 +1901,7 @@ static void __init rcu_init_one(struct rcu_state *rsp, j / rsp->levelspread[i - 1]; } rnp->level = i; - INIT_LIST_HEAD(&rnp->blocked_tasks[0]); - INIT_LIST_HEAD(&rnp->blocked_tasks[1]); - INIT_LIST_HEAD(&rnp->blocked_tasks[2]); - INIT_LIST_HEAD(&rnp->blocked_tasks[3]); + INIT_LIST_HEAD(&rnp->blkd_tasks); } } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index bd891def330..5a439c180e6 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -107,7 +107,7 @@ struct rcu_node { /* an rcu_data structure, otherwise, each */ /* bit corresponds to a child rcu_node */ /* structure. */ - unsigned long expmask; /* Groups that have ->blocked_tasks[] */ + unsigned long expmask; /* Groups that have ->blkd_tasks */ /* elements that need to drain to allow the */ /* current expedited grace period to */ /* complete (only for TREE_PREEMPT_RCU). */ @@ -120,11 +120,20 @@ struct rcu_node { u8 grpnum; /* CPU/group number for next level up. */ u8 level; /* root is at level 0. */ struct rcu_node *parent; - struct list_head blocked_tasks[4]; - /* Tasks blocked in RCU read-side critsect. */ - /* Grace period number (->gpnum) x blocked */ - /* by tasks on the (x & 0x1) element of the */ - /* blocked_tasks[] array. */ + struct list_head blkd_tasks; + /* Tasks blocked in RCU read-side critical */ + /* section. Tasks are placed at the head */ + /* of this list and age towards the tail. */ + struct list_head *gp_tasks; + /* Pointer to the first task blocking the */ + /* current grace period, or NULL if there */ + /* is no such task. */ + struct list_head *exp_tasks; + /* Pointer to the first task blocking the */ + /* current expedited grace period, or NULL */ + /* if there is no such task. If there */ + /* is no current expedited grace period, */ + /* then there can cannot be any such task. */ } ____cacheline_internodealigned_in_smp; /* diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 764b5fcc7c5..774f010a461 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -130,12 +130,12 @@ static void rcu_preempt_qs(int cpu) * We have entered the scheduler, and the current task might soon be * context-switched away from. If this task is in an RCU read-side * critical section, we will no longer be able to rely on the CPU to - * record that fact, so we enqueue the task on the appropriate entry - * of the blocked_tasks[] array. The task will dequeue itself when - * it exits the outermost enclosing RCU read-side critical section. - * Therefore, the current grace period cannot be permitted to complete - * until the blocked_tasks[] entry indexed by the low-order bit of - * rnp->gpnum empties. + * record that fact, so we enqueue the task on the blkd_tasks list. + * The task will dequeue itself when it exits the outermost enclosing + * RCU read-side critical section. Therefore, the current grace period + * cannot be permitted to complete until the blkd_tasks list entries + * predating the current grace period drain, in other words, until + * rnp->gp_tasks becomes NULL. * * Caller must disable preemption. */ @@ -143,7 +143,6 @@ static void rcu_preempt_note_context_switch(int cpu) { struct task_struct *t = current; unsigned long flags; - int phase; struct rcu_data *rdp; struct rcu_node *rnp; @@ -165,15 +164,26 @@ static void rcu_preempt_note_context_switch(int cpu) * (i.e., this CPU has not yet passed through a quiescent * state for the current grace period), then as long * as that task remains queued, the current grace period - * cannot end. + * cannot end. Note that there is some uncertainty as + * to exactly when the current grace period started. + * We take a conservative approach, which can result + * in unnecessarily waiting on tasks that started very + * slightly after the current grace period began. C'est + * la vie!!! * * But first, note that the current CPU must still be * on line! */ WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); - phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1; - list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); + if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { + list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); + rnp->gp_tasks = &t->rcu_node_entry; + } else { + list_add(&t->rcu_node_entry, &rnp->blkd_tasks); + if (rnp->qsmask & rdp->grpmask) + rnp->gp_tasks = &t->rcu_node_entry; + } raw_spin_unlock_irqrestore(&rnp->lock, flags); } @@ -210,10 +220,7 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock); */ static int rcu_preempted_readers(struct rcu_node *rnp) { - int phase = rnp->gpnum & 0x1; - - return !list_empty(&rnp->blocked_tasks[phase]) || - !list_empty(&rnp->blocked_tasks[phase + 2]); + return rnp->gp_tasks != NULL; } /* @@ -253,6 +260,21 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) } /* + * Advance a ->blkd_tasks-list pointer to the next entry, instead + * returning NULL if at the end of the list. + */ +static struct list_head *rcu_next_node_entry(struct task_struct *t, + struct rcu_node *rnp) +{ + struct list_head *np; + + np = t->rcu_node_entry.next; + if (np == &rnp->blkd_tasks) + np = NULL; + return np; +} + +/* * Handle special cases during rcu_read_unlock(), such as needing to * notify RCU core processing or task having blocked during the RCU * read-side critical section. @@ -262,6 +284,7 @@ static void rcu_read_unlock_special(struct task_struct *t) int empty; int empty_exp; unsigned long flags; + struct list_head *np; struct rcu_node *rnp; int special; @@ -305,7 +328,12 @@ static void rcu_read_unlock_special(struct task_struct *t) empty = !rcu_preempted_readers(rnp); empty_exp = !rcu_preempted_readers_exp(rnp); smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ + np = rcu_next_node_entry(t, rnp); list_del_init(&t->rcu_node_entry); + if (&t->rcu_node_entry == rnp->gp_tasks) + rnp->gp_tasks = np; + if (&t->rcu_node_entry == rnp->exp_tasks) + rnp->exp_tasks = np; t->rcu_blocked_node = NULL; /* @@ -361,18 +389,16 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock); static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) { unsigned long flags; - struct list_head *lp; - int phase; struct task_struct *t; - if (rcu_preempted_readers(rnp)) { - raw_spin_lock_irqsave(&rnp->lock, flags); - phase = rnp->gpnum & 0x1; - lp = &rnp->blocked_tasks[phase]; - list_for_each_entry(t, lp, rcu_node_entry) - sched_show_task(t); - raw_spin_unlock_irqrestore(&rnp->lock, flags); - } + if (!rcu_preempted_readers(rnp)) + return; + raw_spin_lock_irqsave(&rnp->lock, flags); + t = list_entry(rnp->gp_tasks, + struct task_struct, rcu_node_entry); + list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) + sched_show_task(t); + raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* @@ -402,16 +428,14 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp) */ static void rcu_print_task_stall(struct rcu_node *rnp) { - struct list_head *lp; - int phase; struct task_struct *t; - if (rcu_preempted_readers(rnp)) { - phase = rnp->gpnum & 0x1; - lp = &rnp->blocked_tasks[phase]; - list_for_each_entry(t, lp, rcu_node_entry) - printk(" P%d", t->pid); - } + if (!rcu_preempted_readers(rnp)) + return; + t = list_entry(rnp->gp_tasks, + struct task_struct, rcu_node_entry); + list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) + printk(" P%d", t->pid); } /* @@ -430,10 +454,15 @@ static void rcu_preempt_stall_reset(void) * period that still has RCU readers blocked! This function must be * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock * must be held by the caller. + * + * Also, if there are blocked tasks on the list, they automatically + * block the newly created grace period, so set up ->gp_tasks accordingly. */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) { WARN_ON_ONCE(rcu_preempted_readers(rnp)); + if (!list_empty(&rnp->blkd_tasks)) + rnp->gp_tasks = rnp->blkd_tasks.next; WARN_ON_ONCE(rnp->qsmask); } @@ -457,45 +486,49 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { - int i; struct list_head *lp; struct list_head *lp_root; int retval = 0; struct rcu_node *rnp_root = rcu_get_root(rsp); - struct task_struct *tp; + struct task_struct *t; if (rnp == rnp_root) { WARN_ONCE(1, "Last CPU thought to be offlined?"); return 0; /* Shouldn't happen: at least one CPU online. */ } - WARN_ON_ONCE(rnp != rdp->mynode && - (!list_empty(&rnp->blocked_tasks[0]) || - !list_empty(&rnp->blocked_tasks[1]) || - !list_empty(&rnp->blocked_tasks[2]) || - !list_empty(&rnp->blocked_tasks[3]))); + + /* If we are on an internal node, complain bitterly. */ + WARN_ON_ONCE(rnp != rdp->mynode); /* - * Move tasks up to root rcu_node. Rely on the fact that the - * root rcu_node can be at most one ahead of the rest of the - * rcu_nodes in terms of gp_num value. This fact allows us to - * move the blocked_tasks[] array directly, element by element. + * Move tasks up to root rcu_node. Don't try to get fancy for + * this corner-case operation -- just put this node's tasks + * at the head of the root node's list, and update the root node's + * ->gp_tasks and ->exp_tasks pointers to those of this node's, + * if non-NULL. This might result in waiting for more tasks than + * absolutely necessary, but this is a good performance/complexity + * tradeoff. */ if (rcu_preempted_readers(rnp)) retval |= RCU_OFL_TASKS_NORM_GP; if (rcu_preempted_readers_exp(rnp)) retval |= RCU_OFL_TASKS_EXP_GP; - for (i = 0; i < 4; i++) { - lp = &rnp->blocked_tasks[i]; - lp_root = &rnp_root->blocked_tasks[i]; - while (!list_empty(lp)) { - tp = list_entry(lp->next, typeof(*tp), rcu_node_entry); - raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ - list_del(&tp->rcu_node_entry); - tp->rcu_blocked_node = rnp_root; - list_add(&tp->rcu_node_entry, lp_root); - raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */ - } + lp = &rnp->blkd_tasks; + lp_root = &rnp_root->blkd_tasks; + while (!list_empty(lp)) { + t = list_entry(lp->next, typeof(*t), rcu_node_entry); + raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ + list_del(&t->rcu_node_entry); + t->rcu_blocked_node = rnp_root; + list_add(&t->rcu_node_entry, lp_root); + if (&t->rcu_node_entry == rnp->gp_tasks) + rnp_root->gp_tasks = rnp->gp_tasks; + if (&t->rcu_node_entry == rnp->exp_tasks) + rnp_root->exp_tasks = rnp->exp_tasks; + raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ } + rnp->gp_tasks = NULL; + rnp->exp_tasks = NULL; return retval; } @@ -586,8 +619,7 @@ static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); */ static int rcu_preempted_readers_exp(struct rcu_node *rnp) { - return !list_empty(&rnp->blocked_tasks[2]) || - !list_empty(&rnp->blocked_tasks[3]); + return rnp->exp_tasks != NULL; } /* @@ -647,12 +679,13 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) static void sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) { - int must_wait; + int must_wait = 0; raw_spin_lock(&rnp->lock); /* irqs already disabled */ - list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]); - list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]); - must_wait = rcu_preempted_readers_exp(rnp); + if (!list_empty(&rnp->blkd_tasks)) { + rnp->exp_tasks = rnp->blkd_tasks.next; + must_wait = 1; + } raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ if (!must_wait) rcu_report_exp_rnp(rsp, rnp); @@ -661,9 +694,7 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) /* * Wait for an rcu-preempt grace period, but expedite it. The basic idea * is to invoke synchronize_sched_expedited() to push all the tasks to - * the ->blocked_tasks[] lists, move all entries from the first set of - * ->blocked_tasks[] lists to the second set, and finally wait for this - * second set to drain. + * the ->blkd_tasks lists and wait for this list to drain. */ void synchronize_rcu_expedited(void) { @@ -695,7 +726,7 @@ void synchronize_rcu_expedited(void) if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) goto unlock_mb_ret; /* Others did our work for us. */ - /* force all RCU readers onto blocked_tasks[]. */ + /* force all RCU readers onto ->blkd_tasks lists. */ synchronize_sched_expedited(); raw_spin_lock_irqsave(&rsp->onofflock, flags); @@ -707,7 +738,7 @@ void synchronize_rcu_expedited(void) raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } - /* Snapshot current state of ->blocked_tasks[] lists. */ + /* Snapshot current state of ->blkd_tasks lists. */ rcu_for_each_leaf_node(rsp, rnp) sync_rcu_preempt_exp_init(rsp, rnp); if (NUM_RCU_NODES > 1) @@ -715,7 +746,7 @@ void synchronize_rcu_expedited(void) raw_spin_unlock_irqrestore(&rsp->onofflock, flags); - /* Wait for snapshotted ->blocked_tasks[] lists to drain. */ + /* Wait for snapshotted ->blkd_tasks lists to drain. */ rnp = rcu_get_root(rsp); wait_event(sync_rcu_preempt_exp_wq, sync_rcu_preempt_exp_done(rnp)); diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index 4a21ca55ef7..1cedf94e2c4 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -161,7 +161,6 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp) { unsigned long gpnum; int level = 0; - int phase; struct rcu_node *rnp; gpnum = rsp->gpnum; @@ -178,13 +177,11 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp) seq_puts(m, "\n"); level = rnp->level; } - phase = gpnum & 0x1; - seq_printf(m, "%lx/%lx %c%c>%c%c %d:%d ^%d ", + seq_printf(m, "%lx/%lx %c%c>%c %d:%d ^%d ", rnp->qsmask, rnp->qsmaskinit, - "T."[list_empty(&rnp->blocked_tasks[phase])], - "E."[list_empty(&rnp->blocked_tasks[phase + 2])], - "T."[list_empty(&rnp->blocked_tasks[!phase])], - "E."[list_empty(&rnp->blocked_tasks[!phase + 2])], + ".G"[rnp->gp_tasks != NULL], + ".E"[rnp->exp_tasks != NULL], + ".T"[!list_empty(&rnp->blkd_tasks)], rnp->grplo, rnp->grphi, rnp->grpnum); } seq_puts(m, "\n"); |