1 files changed, 183 insertions, 77 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index e441b77b614e..5b8ad827fd86 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -105,7 +105,7 @@ int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
  * The rcu_scheduler_active variable transitions from zero to one just
  * before the first task is spawned.  So when this variable is zero, RCU
  * can assume that there is but one task, allowing RCU to (for example)
- * optimized synchronize_sched() to a simple barrier().  When this variable
+ * optimize synchronize_sched() to a simple barrier().  When this variable
  * is one, RCU must actually do all the hard work required to detect real
  * grace periods.  This variable is also used to suppress boot-time false
  * positives from lockdep-RCU error checking.
@@ -217,12 +217,6 @@ module_param(blimit, long, 0444);
 module_param(qhimark, long, 0444);
 module_param(qlowmark, long, 0444);
 
-int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
-int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
-
-module_param(rcu_cpu_stall_suppress, int, 0644);
-module_param(rcu_cpu_stall_timeout, int, 0644);
-
 static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS;
 static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS;
 
@@ -305,17 +299,27 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
 }
 
 /*
- * Does the current CPU require a yet-as-unscheduled grace period?
+ * Does the current CPU require a not-yet-started grace period?
+ * The caller must have disabled interrupts to prevent races with
+ * normal callback registry.
  */
 static int
 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-        struct rcu_head **ntp;
+        int i;
 
-        ntp = rdp->nxttail[RCU_DONE_TAIL +
-                           (ACCESS_ONCE(rsp->completed) != rdp->completed)];
-        return rdp->nxttail[RCU_DONE_TAIL] && ntp && *ntp &&
-               !rcu_gp_in_progress(rsp);
+        if (rcu_gp_in_progress(rsp))
+                return 0;  /* No, a grace period is already in progress. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL])
+                return 0;  /* No, this is a no-CBs (or offline) CPU. */
+        if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
+                return 1;  /* Yes, this CPU has newly registered callbacks. */
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+                if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
+                    ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
+                                 rdp->nxtcompleted[i]))
+                        return 1;  /* Yes, CBs for future grace period. */
+        return 0; /* No grace period needed. */
 }
 
 /*
@@ -336,7 +340,7 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
                                 bool user)
 {
-        trace_rcu_dyntick("Start", oldval, 0);
+        trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
         if (!user && !is_idle_task(current)) {
                 struct task_struct *idle = idle_task(smp_processor_id());
 
@@ -727,7 +731,7 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
  * interrupt from idle, return true.  The caller must have at least
  * disabled preemption.
  */
-int rcu_is_cpu_rrupt_from_idle(void)
+static int rcu_is_cpu_rrupt_from_idle(void)
 {
         return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
 }
@@ -793,28 +797,10 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
         return 0;
 }
 
-static int jiffies_till_stall_check(void)
-{
-        int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
-
-        /*
-         * Limit check must be consistent with the Kconfig limits
-         * for CONFIG_RCU_CPU_STALL_TIMEOUT.
-         */
-        if (till_stall_check < 3) {
-                ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
-                till_stall_check = 3;
-        } else if (till_stall_check > 300) {
-                ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
-                till_stall_check = 300;
-        }
-        return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
-}
-
 static void record_gp_stall_check_time(struct rcu_state *rsp)
 {
         rsp->gp_start = jiffies;
-        rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
+        rsp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
 }
 
 /*
@@ -857,7 +843,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
                 return;
         }
-        rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
+        rsp->jiffies_stall = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
         /*
@@ -935,7 +921,7 @@ static void print_cpu_stall(struct rcu_state *rsp)
         raw_spin_lock_irqsave(&rnp->lock, flags);
         if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
                 rsp->jiffies_stall = jiffies +
-                                     3 * jiffies_till_stall_check() + 3;
+                                     3 * rcu_jiffies_till_stall_check() + 3;
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
         set_need_resched();  /* kick ourselves to get things going. */
@@ -966,12 +952,6 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
         }
 }
 
-static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
-{
-        rcu_cpu_stall_suppress = 1;
-        return NOTIFY_DONE;
-}
-
 /**
  * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
  *
@@ -989,15 +969,6 @@ void rcu_cpu_stall_reset(void)
                 rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
 }
 
-static struct notifier_block rcu_panic_block = {
-        .notifier_call = rcu_panic,
-};
-
-static void __init check_cpu_stall_init(void)
-{
-        atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
-}
-
 /*
  * Update CPU-local rcu_data state to record the newly noticed grace period.
  * This is used both when we started the grace period and when we notice
@@ -1071,6 +1042,145 @@ static void init_callback_list(struct rcu_data *rdp)
 }
 
 /*
+ * Determine the value that ->completed will have at the end of the
+ * next subsequent grace period.  This is used to tag callbacks so that
+ * a CPU can invoke callbacks in a timely fashion even if that CPU has
+ * been dyntick-idle for an extended period with callbacks under the
+ * influence of RCU_FAST_NO_HZ.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
+                                       struct rcu_node *rnp)
+{
+        /*
+         * If RCU is idle, we just wait for the next grace period.
+         * But we can only be sure that RCU is idle if we are looking
+         * at the root rcu_node structure -- otherwise, a new grace
+         * period might have started, but just not yet gotten around
+         * to initializing the current non-root rcu_node structure.
+         */
+        if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
+                return rnp->completed + 1;
+
+        /*
+         * Otherwise, wait for a possible partial grace period and
+         * then the subsequent full grace period.
+         */
+        return rnp->completed + 2;
+}
+
+/*
+ * If there is room, assign a ->completed number to any callbacks on
+ * this CPU that have not already been assigned.  Also accelerate any
+ * callbacks that were previously assigned a ->completed number that has
+ * since proven to be too conservative, which can happen if callbacks get
+ * assigned a ->completed number while RCU is idle, but with reference to
+ * a non-root rcu_node structure.  This function is idempotent, so it does
+ * not hurt to call it repeatedly.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
+                               struct rcu_data *rdp)
+{
+        unsigned long c;
+        int i;
+
+        /* If the CPU has no callbacks, nothing to do. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+                return;
+
+        /*
+         * Starting from the sublist containing the callbacks most
+         * recently assigned a ->completed number and working down, find the
+         * first sublist that is not assignable to an upcoming grace period.
+         * Such a sublist has something in it (first two tests) and has
+         * a ->completed number assigned that will complete sooner than
+         * the ->completed number for newly arrived callbacks (last test).
+         *
+         * The key point is that any later sublist can be assigned the
+         * same ->completed number as the newly arrived callbacks, which
+         * means that the callbacks in any of these later sublist can be
+         * grouped into a single sublist, whether or not they have already
+         * been assigned a ->completed number.
+         */
+        c = rcu_cbs_completed(rsp, rnp);
+        for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
+                if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
+                    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
+                        break;
+
+        /*
+         * If there are no sublist for unassigned callbacks, leave.
+         * At the same time, advance "i" one sublist, so that "i" will
+         * index into the sublist where all the remaining callbacks should
+         * be grouped into.
+         */
+        if (++i >= RCU_NEXT_TAIL)
+                return;
+
+        /*
+         * Assign all subsequent callbacks' ->completed number to the next
+         * full grace period and group them all in the sublist initially
+         * indexed by "i".
+         */
+        for (; i <= RCU_NEXT_TAIL; i++) {
+                rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
+                rdp->nxtcompleted[i] = c;
+        }
+
+        /* Trace depending on how much we were able to accelerate. */
+        if (!*rdp->nxttail[RCU_WAIT_TAIL])
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, "AccWaitCB");
+        else
+                trace_rcu_grace_period(rsp->name, rdp->gpnum, "AccReadyCB");
+}
+
+/*
+ * Move any callbacks whose grace period has completed to the
+ * RCU_DONE_TAIL sublist, then compact the remaining sublists and
+ * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
+ * sublist.  This function is idempotent, so it does not hurt to
+ * invoke it repeatedly.  As long as it is not invoked -too- often...
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static void rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
+                            struct rcu_data *rdp)
+{
+        int i, j;
+
+        /* If the CPU has no callbacks, nothing to do. */
+        if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+                return;
+
+        /*
+         * Find all callbacks whose ->completed numbers indicate that they
+         * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
+         */
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+                if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
+                        break;
+                rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
+        }
+        /* Clean up any sublist tail pointers that were misordered above. */
+        for (j = RCU_WAIT_TAIL; j < i; j++)
+                rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
+
+        /* Copy down callbacks to fill in empty sublists. */
+        for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+                if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
+                        break;
+                rdp->nxttail[j] = rdp->nxttail[i];
+                rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
+        }
+
+        /* Classify any remaining callbacks. */
+        rcu_accelerate_cbs(rsp, rnp, rdp);
+}
+
+/*
  * Advance this CPU's callbacks, but only if the current grace period
  * has ended.  This may be called only from the CPU to whom the rdp
  * belongs.  In addition, the corresponding leaf rcu_node structure's
@@ -1080,12 +1190,15 @@ static void
 __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
 {
         /* Did another grace period end? */
-        if (rdp->completed != rnp->completed) {
+        if (rdp->completed == rnp->completed) {
 
-                /* Advance callbacks.  No harm if list empty. */
-                rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
-                rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
-                rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+                /* No, so just accelerate recent callbacks. */
+                rcu_accelerate_cbs(rsp, rnp, rdp);
+
+        } else {
+
+                /* Advance callbacks. */
+                rcu_advance_cbs(rsp, rnp, rdp);
 
                 /* Remember that we saw this grace-period completion. */
                 rdp->completed = rnp->completed;
@@ -1392,17 +1505,10 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
         /*
          * Because there is no grace period in progress right now,
          * any callbacks we have up to this point will be satisfied
-         * by the next grace period.  So promote all callbacks to be
-         * handled after the end of the next grace period.  If the
-         * CPU is not yet aware of the end of the previous grace period,
-         * we need to allow for the callback advancement that will
-         * occur when it does become aware.  Deadlock prevents us from
-         * making it aware at this point: We cannot acquire a leaf
-         * rcu_node ->lock while holding the root rcu_node ->lock.
+         * by the next grace period.  So this is a good place to
+         * assign a grace period number to recently posted callbacks.
          */
-        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
-        if (rdp->completed == rsp->completed)
-                rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+        rcu_accelerate_cbs(rsp, rnp, rdp);
 
         rsp->gp_flags = RCU_GP_FLAG_INIT;
         raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */
@@ -1527,7 +1633,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
                  * This GP can't end until cpu checks in, so all of our
                  * callbacks can be processed during the next GP.
                  */
-                rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+                rcu_accelerate_cbs(rsp, rnp, rdp);
 
                 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
         }
@@ -1779,7 +1885,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
         long bl, count, count_lazy;
         int i;
 
-        /* If no callbacks are ready, just return.*/
+        /* If no callbacks are ready, just return. */
         if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
                 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
                 trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
@@ -2008,19 +2114,19 @@ __rcu_process_callbacks(struct rcu_state *rsp)
 
         WARN_ON_ONCE(rdp->beenonline == 0);
 
-        /*
-         * Advance callbacks in response to end of earlier grace
-         * period that some other CPU ended.
-         */
+        /* Handle the end of a grace period that some other CPU ended.  */
         rcu_process_gp_end(rsp, rdp);
 
         /* Update RCU state based on any recent quiescent states. */
         rcu_check_quiescent_state(rsp, rdp);
 
         /* Does this CPU require a not-yet-started grace period? */
+        local_irq_save(flags);
         if (cpu_needs_another_gp(rsp, rdp)) {
-                raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
+                raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
                 rcu_start_gp(rsp, flags);  /* releases above lock */
+        } else {
+                local_irq_restore(flags);
         }
 
         /* If there are callbacks ready, invoke them. */
@@ -2719,9 +2825,6 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
         WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
         WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
-#ifdef CONFIG_RCU_USER_QS
-        WARN_ON_ONCE(rdp->dynticks->in_user);
-#endif
         rdp->cpu = cpu;
         rdp->rsp = rsp;
         rcu_boot_init_nocb_percpu_data(rdp);
@@ -2938,6 +3041,10 @@ static void __init rcu_init_one(struct rcu_state *rsp,
 
         BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
 
+        /* Silence gcc 4.8 warning about array index out of range. */
+        if (rcu_num_lvls > RCU_NUM_LVLS)
+                panic("rcu_init_one: rcu_num_lvls overflow");
+
         /* Initialize the level-tracking arrays. */
 
         for (i = 0; i < rcu_num_lvls; i++)
@@ -3074,7 +3181,6 @@ void __init rcu_init(void)
         cpu_notifier(rcu_cpu_notify, 0);
         for_each_online_cpu(cpu)
                 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
-        check_cpu_stall_init();
 }
 
 #include "rcutree_plugin.h"