Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The main changes in this cycle are:

   - Documentation updates

   - RCU CPU stall-warning updates

   - Torture-test updates

   - Miscellaneous fixes

  Size wise the biggest updates are to documentation. Excluding
  documentation most of the code increase comes from a single commit
  which expands debugging"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
  srcu: Add parameters to SRCU docbook comments
  doc: Rewrite confusing statement about memory barriers
  memory-barriers.txt: Fix typo in pairing example
  rcu/segcblist: Include rcupdate.h
  rcu: Add extended-quiescent-state testing advice
  rcu: Suppress lockdep false-positive ->boost_mtx complaints
  rcu: Do not include rtmutex_common.h unconditionally
  torture: Provide TMPDIR environment variable to specify tmpdir
  rcutorture: Dump writer stack if stalled
  rcutorture: Add interrupt-disable capability to stall-warning tests
  rcu: Suppress RCU CPU stall warnings while dumping trace
  rcu: Turn off tracing before dumping trace
  rcu: Make RCU CPU stall warnings check for irq-disabled CPUs
  sched,rcu: Make cond_resched() provide RCU quiescent state
  sched: Make resched_cpu() unconditional
  irq_work: Map irq_work_on_queue() to irq_work_on() in !SMP
  rcu: Create call_rcu_tasks() kthread at boot time
  rcu: Fix up pending cbs check in rcu_prepare_for_idle
  memory-barriers: Rework multicopy-atomicity section
  memory-barriers: Replace uses of "transitive"
  ...

1 files changed, 127 insertions, 32 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3e3650e94ae6..e4fe06d42385 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -534,8 +534,8 @@ module_param(rcu_kick_kthreads, bool, 0644);
  * How long the grace period must be before we start recruiting
  * quiescent-state help from rcu_note_context_switch().
  */
-static ulong jiffies_till_sched_qs = HZ / 20;
-module_param(jiffies_till_sched_qs, ulong, 0644);
+static ulong jiffies_till_sched_qs = HZ / 10;
+module_param(jiffies_till_sched_qs, ulong, 0444);
 
 static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
                                   struct rcu_data *rdp);
@@ -837,6 +837,9 @@ static void rcu_eqs_enter(bool user)
  * We crowbar the ->dynticks_nesting field to zero to allow for
  * the possibility of usermode upcalls having messed up our count
  * of interrupt nesting level during the prior busy period.
+ *
+ * If you add or remove a call to rcu_idle_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_idle_enter(void)
 {
@@ -852,6 +855,9 @@ void rcu_idle_enter(void)
  * is permitted between this call and rcu_user_exit(). This way the
  * CPU doesn't need to maintain the tick for RCU maintenance purposes
  * when the CPU runs in userspace.
+ *
+ * If you add or remove a call to rcu_user_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_user_enter(void)
 {
@@ -875,6 +881,9 @@ void rcu_user_enter(void)
  * Use things like work queues to work around this limitation.
  *
  * You have been warned.
+ *
+ * If you add or remove a call to rcu_irq_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_irq_exit(void)
 {
@@ -899,6 +908,9 @@ void rcu_irq_exit(void)
 
 /*
  * Wrapper for rcu_irq_exit() where interrupts are enabled.
+ *
+ * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_irq_exit_irqson(void)
 {
@@ -971,6 +983,9 @@ static void rcu_eqs_exit(bool user)
  * allow for the possibility of usermode upcalls messing up our count
  * of interrupt nesting level during the busy period that is just
  * now starting.
+ *
+ * If you add or remove a call to rcu_idle_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_idle_exit(void)
 {
@@ -987,6 +1002,9 @@ void rcu_idle_exit(void)
  *
  * Exit RCU idle mode while entering the kernel because it can
  * run a RCU read side critical section anytime.
+ *
+ * If you add or remove a call to rcu_user_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_user_exit(void)
 {
@@ -1012,6 +1030,9 @@ void rcu_user_exit(void)
  * Use things like work queues to work around this limitation.
  *
  * You have been warned.
+ *
+ * If you add or remove a call to rcu_irq_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_irq_enter(void)
 {
@@ -1037,6 +1058,9 @@ void rcu_irq_enter(void)
 
 /*
  * Wrapper for rcu_irq_enter() where interrupts are enabled.
+ *
+ * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_irq_enter_irqson(void)
 {
@@ -1055,6 +1079,9 @@ void rcu_irq_enter_irqson(void)
  * that the CPU is active.  This implementation permits nested NMIs, as
  * long as the nesting level does not overflow an int.  (You will probably
  * run out of stack space first.)
+ *
+ * If you add or remove a call to rcu_nmi_enter(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_nmi_enter(void)
 {
@@ -1087,6 +1114,9 @@ void rcu_nmi_enter(void)
  * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
  * to let the RCU grace-period handling know that the CPU is back to
  * being RCU-idle.
+ *
+ * If you add or remove a call to rcu_nmi_exit(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_nmi_exit(void)
 {
@@ -1207,6 +1237,22 @@ static int rcu_is_cpu_rrupt_from_idle(void)
 }
 
 /*
+ * We are reporting a quiescent state on behalf of some other CPU, so
+ * it is our responsibility to check for and handle potential overflow
+ * of the rcu_node ->gpnum counter with respect to the rcu_data counters.
+ * After all, the CPU might be in deep idle state, and thus executing no
+ * code whatsoever.
+ */
+static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+        lockdep_assert_held(&rnp->lock);
+        if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, rnp->gpnum))
+                WRITE_ONCE(rdp->gpwrap, true);
+        if (ULONG_CMP_LT(rdp->rcu_iw_gpnum + ULONG_MAX / 4, rnp->gpnum))
+                rdp->rcu_iw_gpnum = rnp->gpnum + ULONG_MAX / 4;
+}
+
+/*
  * Snapshot the specified CPU's dynticks counter so that we can later
  * credit them with an implicit quiescent state.  Return 1 if this CPU
  * is in dynticks idle mode, which is an extended quiescent state.
@@ -1216,15 +1262,34 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
         rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
         if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
-                if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
-                                 rdp->mynode->gpnum))
-                        WRITE_ONCE(rdp->gpwrap, true);
+                rcu_gpnum_ovf(rdp->mynode, rdp);
                 return 1;
         }
         return 0;
 }
 
 /*
+ * Handler for the irq_work request posted when a grace period has
+ * gone on for too long, but not yet long enough for an RCU CPU
+ * stall warning.  Set state appropriately, but just complain if
+ * there is unexpected state on entry.
+ */
+static void rcu_iw_handler(struct irq_work *iwp)
+{
+        struct rcu_data *rdp;
+        struct rcu_node *rnp;
+
+        rdp = container_of(iwp, struct rcu_data, rcu_iw);
+        rnp = rdp->mynode;
+        raw_spin_lock_rcu_node(rnp);
+        if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
+                rdp->rcu_iw_gpnum = rnp->gpnum;
+                rdp->rcu_iw_pending = false;
+        }
+        raw_spin_unlock_rcu_node(rnp);
+}
+
+/*
  * Return true if the specified CPU has passed through a quiescent
  * state by virtue of being in or having passed through an dynticks
  * idle state since the last call to dyntick_save_progress_counter()
@@ -1235,8 +1300,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
         unsigned long jtsq;
         bool *rnhqp;
         bool *ruqp;
-        unsigned long rjtsc;
-        struct rcu_node *rnp;
+        struct rcu_node *rnp = rdp->mynode;
 
         /*
          * If the CPU passed through or entered a dynticks idle phase with
@@ -1249,34 +1313,25 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
         if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
                 rdp->dynticks_fqs++;
+                rcu_gpnum_ovf(rnp, rdp);
                 return 1;
         }
 
-        /* Compute and saturate jiffies_till_sched_qs. */
-        jtsq = jiffies_till_sched_qs;
-        rjtsc = rcu_jiffies_till_stall_check();
-        if (jtsq > rjtsc / 2) {
-                WRITE_ONCE(jiffies_till_sched_qs, rjtsc);
-                jtsq = rjtsc / 2;
-        } else if (jtsq < 1) {
-                WRITE_ONCE(jiffies_till_sched_qs, 1);
-                jtsq = 1;
-        }
-
         /*
          * Has this CPU encountered a cond_resched_rcu_qs() since the
          * beginning of the grace period?  For this to be the case,
          * the CPU has to have noticed the current grace period.  This
          * might not be the case for nohz_full CPUs looping in the kernel.
          */
-        rnp = rdp->mynode;
+        jtsq = jiffies_till_sched_qs;
         ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
         if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
             READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
             READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
+                rcu_gpnum_ovf(rnp, rdp);
                 return 1;
-        } else {
+        } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) {
                 /* Load rcu_qs_ctr before store to rcu_urgent_qs. */
                 smp_store_release(ruqp, true);
         }
@@ -1285,6 +1340,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
         if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
                 rdp->offline_fqs++;
+                rcu_gpnum_ovf(rnp, rdp);
                 return 1;
         }
 
@@ -1304,10 +1360,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
          * updates are only once every few jiffies, the probability of
          * lossage (and thus of slight grace-period extension) is
          * quite low.
-         *
-         * Note that if the jiffies_till_sched_qs boot/sysfs parameter
-         * is set too high, we override with half of the RCU CPU stall
-         * warning delay.
          */
         rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
         if (!READ_ONCE(*rnhqp) &&
@@ -1316,15 +1368,26 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
                 WRITE_ONCE(*rnhqp, true);
                 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
                 smp_store_release(ruqp, true);
-                rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
+                rdp->rsp->jiffies_resched += jtsq; /* Re-enable beating. */
         }
 
         /*
-         * If more than halfway to RCU CPU stall-warning time, do
-         * a resched_cpu() to try to loosen things up a bit.
+         * If more than halfway to RCU CPU stall-warning time, do a
+         * resched_cpu() to try to loosen things up a bit.  Also check to
+         * see if the CPU is getting hammered with interrupts, but only
+         * once per grace period, just to keep the IPIs down to a dull roar.
          */
-        if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
+        if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) {
                 resched_cpu(rdp->cpu);
+                if (IS_ENABLED(CONFIG_IRQ_WORK) &&
+                    !rdp->rcu_iw_pending && rdp->rcu_iw_gpnum != rnp->gpnum &&
+                    (rnp->ffmask & rdp->grpmask)) {
+                        init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
+                        rdp->rcu_iw_pending = true;
+                        rdp->rcu_iw_gpnum = rnp->gpnum;
+                        irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
+                }
+        }
 
         return 0;
 }
@@ -1513,6 +1576,7 @@ static void print_cpu_stall(struct rcu_state *rsp)
 {
         int cpu;
         unsigned long flags;
+        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
         struct rcu_node *rnp = rcu_get_root(rsp);
         long totqlen = 0;
 
@@ -1528,7 +1592,9 @@ static void print_cpu_stall(struct rcu_state *rsp)
          */
         pr_err("INFO: %s self-detected stall on CPU", rsp->name);
         print_cpu_stall_info_begin();
+        raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
         print_cpu_stall_info(rsp, smp_processor_id());
+        raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
         print_cpu_stall_info_end();
         for_each_possible_cpu(cpu)
                 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
@@ -1922,6 +1988,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
                 rdp->core_needs_qs = need_gp;
                 zero_cpu_stall_ticks(rdp);
                 WRITE_ONCE(rdp->gpwrap, false);
+                rcu_gpnum_ovf(rnp, rdp);
         }
         return ret;
 }
@@ -3702,6 +3769,8 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
         rdp->cpu_no_qs.b.norm = true;
         rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
         rdp->core_needs_qs = false;
+        rdp->rcu_iw_pending = false;
+        rdp->rcu_iw_gpnum = rnp->gpnum - 1;
         trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
@@ -3739,10 +3808,24 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
  */
 int rcutree_online_cpu(unsigned int cpu)
 {
-        sync_sched_exp_online_cleanup(cpu);
-        rcutree_affinity_setting(cpu, -1);
+        unsigned long flags;
+        struct rcu_data *rdp;
+        struct rcu_node *rnp;
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                rnp = rdp->mynode;
+                raw_spin_lock_irqsave_rcu_node(rnp, flags);
+                rnp->ffmask |= rdp->grpmask;
+                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+        }
         if (IS_ENABLED(CONFIG_TREE_SRCU))
                 srcu_online_cpu(cpu);
+        if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+                return 0; /* Too early in boot for scheduler work. */
+        sync_sched_exp_online_cleanup(cpu);
+        rcutree_affinity_setting(cpu, -1);
         return 0;
 }
 
@@ -3752,6 +3835,19 @@ int rcutree_online_cpu(unsigned int cpu)
  */
 int rcutree_offline_cpu(unsigned int cpu)
 {
+        unsigned long flags;
+        struct rcu_data *rdp;
+        struct rcu_node *rnp;
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                rnp = rdp->mynode;
+                raw_spin_lock_irqsave_rcu_node(rnp, flags);
+                rnp->ffmask &= ~rdp->grpmask;
+                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+        }
+
         rcutree_affinity_setting(cpu, cpu);
         if (IS_ENABLED(CONFIG_TREE_SRCU))
                 srcu_offline_cpu(cpu);
@@ -4200,8 +4296,7 @@ void __init rcu_init(void)
         for_each_online_cpu(cpu) {
                 rcutree_prepare_cpu(cpu);
                 rcu_cpu_starting(cpu);
-                if (IS_ENABLED(CONFIG_TREE_SRCU))
-                        srcu_online_cpu(cpu);
+                rcutree_online_cpu(cpu);
         }
 }