5 files changed, 260 insertions, 27 deletions

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 3dd0ca23e191..a621a67ef4e3 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -327,6 +327,11 @@ rcu_torture_cb(struct rcu_head *p)
                 cur_ops->deferred_free(rp);
 }
 
+static int rcu_no_completed(void)
+{
+        return 0;
+}
+
 static void rcu_torture_deferred_free(struct rcu_torture *p)
 {
         call_rcu(&p->rtort_rcu, rcu_torture_cb);
@@ -388,6 +393,21 @@ static struct rcu_torture_ops rcu_sync_ops = {
         .name           = "rcu_sync"
 };
 
+static struct rcu_torture_ops rcu_expedited_ops = {
+        .init           = rcu_sync_torture_init,
+        .cleanup        = NULL,
+        .readlock       = rcu_torture_read_lock,
+        .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
+        .readunlock     = rcu_torture_read_unlock,
+        .completed      = rcu_no_completed,
+        .deferred_free  = rcu_sync_torture_deferred_free,
+        .sync           = synchronize_rcu_expedited,
+        .cb_barrier     = NULL,
+        .stats          = NULL,
+        .irq_capable    = 1,
+        .name           = "rcu_expedited"
+};
+
 /*
  * Definitions for rcu_bh torture testing.
  */
@@ -581,11 +601,6 @@ static void sched_torture_read_unlock(int idx)
         preempt_enable();
 }
 
-static int sched_torture_completed(void)
-{
-        return 0;
-}
-
 static void rcu_sched_torture_deferred_free(struct rcu_torture *p)
 {
         call_rcu_sched(&p->rtort_rcu, rcu_torture_cb);
@@ -602,7 +617,7 @@ static struct rcu_torture_ops sched_ops = {
         .readlock       = sched_torture_read_lock,
         .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
         .readunlock     = sched_torture_read_unlock,
-        .completed      = sched_torture_completed,
+        .completed      = rcu_no_completed,
         .deferred_free  = rcu_sched_torture_deferred_free,
         .sync           = sched_torture_synchronize,
         .cb_barrier     = rcu_barrier_sched,
@@ -617,7 +632,7 @@ static struct rcu_torture_ops sched_sync_ops = {
         .readlock       = sched_torture_read_lock,
         .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
         .readunlock     = sched_torture_read_unlock,
-        .completed      = sched_torture_completed,
+        .completed      = rcu_no_completed,
         .deferred_free  = rcu_sync_torture_deferred_free,
         .sync           = sched_torture_synchronize,
         .cb_barrier     = NULL,
@@ -631,7 +646,7 @@ static struct rcu_torture_ops sched_expedited_ops = {
         .readlock       = sched_torture_read_lock,
         .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
         .readunlock     = sched_torture_read_unlock,
-        .completed      = sched_torture_completed,
+        .completed      = rcu_no_completed,
         .deferred_free  = rcu_sync_torture_deferred_free,
         .sync           = synchronize_sched_expedited,
         .cb_barrier     = NULL,
@@ -1116,7 +1131,8 @@ rcu_torture_init(void)
         int cpu;
         int firsterr = 0;
         static struct rcu_torture_ops *torture_ops[] =
-                { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
+                { &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
+                  &rcu_bh_ops, &rcu_bh_sync_ops,
                   &srcu_ops, &srcu_expedited_ops,
                   &sched_ops, &sched_sync_ops, &sched_expedited_ops, };
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d47e03e5792a..53ae9598f798 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -948,7 +948,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
 {
         unsigned long flags;
         unsigned long mask;
-        int need_quiet = 0;
+        int need_report = 0;
         struct rcu_data *rdp = rsp->rda[cpu];
         struct rcu_node *rnp;
 
@@ -967,7 +967,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
                         break;
                 }
                 if (rnp == rdp->mynode)
-                        need_quiet = rcu_preempt_offline_tasks(rsp, rnp, rdp);
+                        need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
                 else
                         spin_unlock(&rnp->lock); /* irqs remain disabled. */
                 mask = rnp->grpmask;
@@ -982,10 +982,12 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
          */
         spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
         rnp = rdp->mynode;
-        if (need_quiet)
+        if (need_report & RCU_OFL_TASKS_NORM_GP)
                 rcu_report_unblock_qs_rnp(rnp, flags);
         else
                 spin_unlock_irqrestore(&rnp->lock, flags);
+        if (need_report & RCU_OFL_TASKS_EXP_GP)
+                rcu_report_exp_rnp(rsp, rnp);
 
         rcu_adopt_orphan_cbs(rsp);
 }
@@ -1843,6 +1845,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
                         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]);
                 }
         }
 }
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index df2e0b694744..d2a0046f63b2 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -104,8 +104,12 @@ 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[] */
+                                /*  elements that need to drain to allow the */
+                                /*  current expedited grace period to */
+                                /*  complete (only for TREE_PREEMPT_RCU). */
         unsigned long qsmaskinit;
-                                /* Per-GP initialization for qsmask. */
+                                /* Per-GP initial value for qsmask & expmask. */
         unsigned long grpmask;  /* Mask to apply to parent qsmask. */
                                 /*  Only one bit will be set in this mask. */
         int     grplo;          /* lowest-numbered CPU or group here. */
@@ -113,7 +117,7 @@ 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[2];
+        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 */
@@ -128,6 +132,21 @@ struct rcu_node {
         for ((rnp) = &(rsp)->node[0]; \
              (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
 
+/*
+ * Do a breadth-first scan of the non-leaf rcu_node structures for the
+ * specified rcu_state structure.  Note that if there is a singleton
+ * rcu_node tree with but one rcu_node structure, this loop is a no-op.
+ */
+#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
+        for ((rnp) = &(rsp)->node[0]; \
+             (rnp) < (rsp)->level[NUM_RCU_LVLS - 1]; (rnp)++)
+
+/*
+ * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
+ * structure.  Note that if there is a singleton rcu_node tree with but
+ * one rcu_node structure, this loop -will- visit the rcu_node structure.
+ * It is still a leaf node, even if it is also the root node.
+ */
 #define rcu_for_each_leaf_node(rsp, rnp) \
         for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \
              (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
@@ -261,7 +280,7 @@ struct rcu_state {
         long    gpnum;                          /* Current gp number. */
         long    completed;                      /* # of last completed gp. */
 
-        /* End  of fields guarded by root rcu_node's lock. */
+        /* End of fields guarded by root rcu_node's lock. */
 
         spinlock_t onofflock;                   /* exclude on/offline and */
                                                 /*  starting new GP.  Also */
@@ -293,6 +312,13 @@ struct rcu_state {
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 };
 
+/* Return values for rcu_preempt_offline_tasks(). */
+
+#define RCU_OFL_TASKS_NORM_GP   0x1             /* Tasks blocking normal */
+                                                /*  GP were moved to root. */
+#define RCU_OFL_TASKS_EXP_GP    0x2             /* Tasks blocking expedited */
+                                                /*  GP were moved to root. */
+
 #ifdef RCU_TREE_NONCORE
 
 /*
@@ -333,6 +359,9 @@ static void rcu_preempt_offline_cpu(int cpu);
 static void rcu_preempt_check_callbacks(int cpu);
 static void rcu_preempt_process_callbacks(void);
 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
+#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
 static int rcu_preempt_pending(int cpu);
 static int rcu_preempt_needs_cpu(int cpu);
 static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c9f0c975c003..37fbccdf41d5 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -24,12 +24,15 @@
  *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  */
 
+#include <linux/delay.h>
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
 struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
 
+static int rcu_preempted_readers_exp(struct rcu_node *rnp);
+
 /*
  * Tell them what RCU they are running.
  */
@@ -157,7 +160,10 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
  */
 static int rcu_preempted_readers(struct rcu_node *rnp)
 {
-        return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
+        int phase = rnp->gpnum & 0x1;
+
+        return !list_empty(&rnp->blocked_tasks[phase]) ||
+               !list_empty(&rnp->blocked_tasks[phase + 2]);
 }
 
 /*
@@ -204,6 +210,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
 static void rcu_read_unlock_special(struct task_struct *t)
 {
         int empty;
+        int empty_exp;
         unsigned long flags;
         struct rcu_node *rnp;
         int special;
@@ -247,6 +254,8 @@ static void rcu_read_unlock_special(struct task_struct *t)
                         spin_unlock(&rnp->lock);  /* irqs remain disabled. */
                 }
                 empty = !rcu_preempted_readers(rnp);
+                empty_exp = !rcu_preempted_readers_exp(rnp);
+                smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
                 list_del_init(&t->rcu_node_entry);
                 t->rcu_blocked_node = NULL;
 
@@ -259,6 +268,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
                         spin_unlock_irqrestore(&rnp->lock, flags);
                 else
                         rcu_report_unblock_qs_rnp(rnp, flags);
+
+                /*
+                 * If this was the last task on the expedited lists,
+                 * then we need to report up the rcu_node hierarchy.
+                 */
+                if (!empty_exp && !rcu_preempted_readers_exp(rnp))
+                        rcu_report_exp_rnp(&rcu_preempt_state, rnp);
         } else {
                 local_irq_restore(flags);
         }
@@ -343,7 +359,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
         int i;
         struct list_head *lp;
         struct list_head *lp_root;
-        int retval;
+        int retval = 0;
         struct rcu_node *rnp_root = rcu_get_root(rsp);
         struct task_struct *tp;
 
@@ -353,7 +369,9 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
         }
         WARN_ON_ONCE(rnp != rdp->mynode &&
                      (!list_empty(&rnp->blocked_tasks[0]) ||
-                      !list_empty(&rnp->blocked_tasks[1])));
+                      !list_empty(&rnp->blocked_tasks[1]) ||
+                      !list_empty(&rnp->blocked_tasks[2]) ||
+                      !list_empty(&rnp->blocked_tasks[3])));
 
         /*
          * Move tasks up to root rcu_node.  Rely on the fact that the
@@ -361,8 +379,11 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
          * rcu_nodes in terms of gp_num value.  This fact allows us to
          * move the blocked_tasks[] array directly, element by element.
          */
-        retval = rcu_preempted_readers(rnp);
-        for (i = 0; i < 2; i++) {
+        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)) {
@@ -449,14 +470,159 @@ void synchronize_rcu(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
+static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
+static long sync_rcu_preempt_exp_count;
+static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
+
+/*
+ * Return non-zero if there are any tasks in RCU read-side critical
+ * sections blocking the current preemptible-RCU expedited grace period.
+ * If there is no preemptible-RCU expedited grace period currently in
+ * progress, returns zero unconditionally.
+ */
+static int rcu_preempted_readers_exp(struct rcu_node *rnp)
+{
+        return !list_empty(&rnp->blocked_tasks[2]) ||
+               !list_empty(&rnp->blocked_tasks[3]);
+}
+
+/*
+ * return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period.  Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+        return !rcu_preempted_readers_exp(rnp) &&
+               ACCESS_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period.  This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree.  (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        unsigned long flags;
+        unsigned long mask;
+
+        spin_lock_irqsave(&rnp->lock, flags);
+        for (;;) {
+                if (!sync_rcu_preempt_exp_done(rnp))
+                        break;
+                if (rnp->parent == NULL) {
+                        wake_up(&sync_rcu_preempt_exp_wq);
+                        break;
+                }
+                mask = rnp->grpmask;
+                spin_unlock(&rnp->lock); /* irqs remain disabled */
+                rnp = rnp->parent;
+                spin_lock(&rnp->lock); /* irqs already disabled */
+                rnp->expmask &= ~mask;
+        }
+        spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Snapshot the tasks blocking the newly started preemptible-RCU expedited
+ * grace period for the specified rcu_node structure.  If there are no such
+ * tasks, report it up the rcu_node hierarchy.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
+ */
+static void
+sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        int must_wait;
+
+        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);
+        spin_unlock(&rnp->lock); /* irqs remain disabled */
+        if (!must_wait)
+                rcu_report_exp_rnp(rsp, rnp);
+}
+
 /*
- * Wait for an rcu-preempt grace period.  We are supposed to expedite the
- * grace period, but this is the crude slow compatability hack, so just
- * invoke synchronize_rcu().
+ * 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.
  */
 void synchronize_rcu_expedited(void)
 {
-        synchronize_rcu();
+        unsigned long flags;
+        struct rcu_node *rnp;
+        struct rcu_state *rsp = &rcu_preempt_state;
+        long snap;
+        int trycount = 0;
+
+        smp_mb(); /* Caller's modifications seen first by other CPUs. */
+        snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
+        smp_mb(); /* Above access cannot bleed into critical section. */
+
+        /*
+         * Acquire lock, falling back to synchronize_rcu() if too many
+         * lock-acquisition failures.  Of course, if someone does the
+         * expedited grace period for us, just leave.
+         */
+        while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
+                if (trycount++ < 10)
+                        udelay(trycount * num_online_cpus());
+                else {
+                        synchronize_rcu();
+                        return;
+                }
+                if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
+                        goto mb_ret; /* Others did our work for us. */
+        }
+        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[]. */
+        synchronize_sched_expedited();
+
+        spin_lock_irqsave(&rsp->onofflock, flags);
+
+        /* Initialize ->expmask for all non-leaf rcu_node structures. */
+        rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
+                spin_lock(&rnp->lock); /* irqs already disabled. */
+                rnp->expmask = rnp->qsmaskinit;
+                spin_unlock(&rnp->lock); /* irqs remain disabled. */
+        }
+
+        /* Snapshot current state of ->blocked_tasks[] lists. */
+        rcu_for_each_leaf_node(rsp, rnp)
+                sync_rcu_preempt_exp_init(rsp, rnp);
+        if (NUM_RCU_NODES > 1)
+                sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
+
+        spin_unlock_irqrestore(&rsp->onofflock, flags);
+
+        /* Wait for snapshotted ->blocked_tasks[] lists to drain. */
+        rnp = rcu_get_root(rsp);
+        wait_event(sync_rcu_preempt_exp_wq,
+                   sync_rcu_preempt_exp_done(rnp));
+
+        /* Clean up and exit. */
+        smp_mb(); /* ensure expedited GP seen before counter increment. */
+        ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
+unlock_mb_ret:
+        mutex_unlock(&sync_rcu_preempt_exp_mutex);
+mb_ret:
+        smp_mb(); /* ensure subsequent action seen after grace period. */
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 
@@ -655,6 +821,20 @@ void synchronize_rcu_expedited(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Because preemptable RCU does not exist, there is never any need to
+ * report on tasks preempted in RCU read-side critical sections during
+ * expedited RCU grace periods.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+        return;
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 /*
  * Because preemptable RCU does not exist, it never has any work to do.
  */
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 1984cdc51e9a..9d2c88423b31 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -157,6 +157,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 {
         long gpnum;
         int level = 0;
+        int phase;
         struct rcu_node *rnp;
 
         gpnum = rsp->gpnum;
@@ -173,10 +174,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
                         seq_puts(m, "\n");
                         level = rnp->level;
                 }
-                seq_printf(m, "%lx/%lx %c>%c %d:%d ^%d    ",
+                phase = gpnum & 0x1;
+                seq_printf(m, "%lx/%lx %c%c>%c%c %d:%d ^%d    ",
                            rnp->qsmask, rnp->qsmaskinit,
-                           "T."[list_empty(&rnp->blocked_tasks[gpnum & 1])],
-                           "T."[list_empty(&rnp->blocked_tasks[!(gpnum & 1)])],
+                           "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])],
                            rnp->grplo, rnp->grphi, rnp->grpnum);
         }
         seq_puts(m, "\n");