Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  signal: align __lock_task_sighand() irq disabling and RCU
  softirq,rcu: Inform RCU of irq_exit() activity
  sched: Add irq_{enter,exit}() to scheduler_ipi()
  rcu: protect __rcu_read_unlock() against scheduler-using irq handlers
  rcu: Streamline code produced by __rcu_read_unlock()
  rcu: Fix RCU_BOOST race handling current->rcu_read_unlock_special
  rcu: decrease rcu_report_exp_rnp coupling with scheduler

5 files changed, 103 insertions, 28 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index bde99d5358dc..14a6c7b545de 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1260,6 +1260,9 @@ struct task_struct {
 #ifdef CONFIG_PREEMPT_RCU
         int rcu_read_lock_nesting;
         char rcu_read_unlock_special;
+#if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU)
+        int rcu_boosted;
+#endif /* #if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU) */
         struct list_head rcu_node_entry;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 #ifdef CONFIG_TREE_PREEMPT_RCU
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 75113cb7c4fb..8aafbb80b8b0 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -68,6 +68,7 @@ struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
 static struct rcu_state *rcu_state = &rcu_preempt_state;
 
+static void rcu_read_unlock_special(struct task_struct *t);
 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
 
 /*
@@ -147,7 +148,7 @@ static void rcu_preempt_note_context_switch(int cpu)
         struct rcu_data *rdp;
         struct rcu_node *rnp;
 
-        if (t->rcu_read_lock_nesting &&
+        if (t->rcu_read_lock_nesting > 0 &&
             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
                 /* Possibly blocking in an RCU read-side critical section. */
@@ -190,6 +191,14 @@ static void rcu_preempt_note_context_switch(int cpu)
                                 rnp->gp_tasks = &t->rcu_node_entry;
                 }
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        } else if (t->rcu_read_lock_nesting < 0 &&
+                   t->rcu_read_unlock_special) {
+
+                /*
+                 * Complete exit from RCU read-side critical section on
+                 * behalf of preempted instance of __rcu_read_unlock().
+                 */
+                rcu_read_unlock_special(t);
         }
 
         /*
@@ -284,7 +293,7 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t,
  * notify RCU core processing or task having blocked during the RCU
  * read-side critical section.
  */
-static void rcu_read_unlock_special(struct task_struct *t)
+static noinline void rcu_read_unlock_special(struct task_struct *t)
 {
         int empty;
         int empty_exp;
@@ -309,7 +318,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
         }
 
         /* Hardware IRQ handlers cannot block. */
-        if (in_irq()) {
+        if (in_irq() || in_serving_softirq()) {
                 local_irq_restore(flags);
                 return;
         }
@@ -342,6 +351,11 @@ static void rcu_read_unlock_special(struct task_struct *t)
 #ifdef CONFIG_RCU_BOOST
                 if (&t->rcu_node_entry == rnp->boost_tasks)
                         rnp->boost_tasks = np;
+                /* Snapshot and clear ->rcu_boosted with rcu_node lock held. */
+                if (t->rcu_boosted) {
+                        special |= RCU_READ_UNLOCK_BOOSTED;
+                        t->rcu_boosted = 0;
+                }
 #endif /* #ifdef CONFIG_RCU_BOOST */
                 t->rcu_blocked_node = NULL;
 
@@ -358,7 +372,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
 #ifdef CONFIG_RCU_BOOST
                 /* Unboost if we were boosted. */
                 if (special & RCU_READ_UNLOCK_BOOSTED) {
-                        t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
                         rt_mutex_unlock(t->rcu_boost_mutex);
                         t->rcu_boost_mutex = NULL;
                 }
@@ -387,13 +400,22 @@ void __rcu_read_unlock(void)
         struct task_struct *t = current;
 
         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
-        --t->rcu_read_lock_nesting;
-        barrier();  /* decrement before load of ->rcu_read_unlock_special */
-        if (t->rcu_read_lock_nesting == 0 &&
-            unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
-                rcu_read_unlock_special(t);
+        if (t->rcu_read_lock_nesting != 1)
+                --t->rcu_read_lock_nesting;
+        else {
+                t->rcu_read_lock_nesting = INT_MIN;
+                barrier();  /* assign before ->rcu_read_unlock_special load */
+                if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+                        rcu_read_unlock_special(t);
+                barrier();  /* ->rcu_read_unlock_special load before assign */
+                t->rcu_read_lock_nesting = 0;
+        }
 #ifdef CONFIG_PROVE_LOCKING
-        WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+        {
+                int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+                WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+        }
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -589,7 +611,8 @@ static void rcu_preempt_check_callbacks(int cpu)
                 rcu_preempt_qs(cpu);
                 return;
         }
-        if (per_cpu(rcu_preempt_data, cpu).qs_pending)
+        if (t->rcu_read_lock_nesting > 0 &&
+            per_cpu(rcu_preempt_data, cpu).qs_pending)
                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }
 
@@ -695,9 +718,12 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
 
         raw_spin_lock_irqsave(&rnp->lock, flags);
         for (;;) {
-                if (!sync_rcu_preempt_exp_done(rnp))
+                if (!sync_rcu_preempt_exp_done(rnp)) {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
                         break;
+                }
                 if (rnp->parent == NULL) {
+                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
                         wake_up(&sync_rcu_preempt_exp_wq);
                         break;
                 }
@@ -707,7 +733,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
                 raw_spin_lock(&rnp->lock); /* irqs already disabled */
                 rnp->expmask &= ~mask;
         }
-        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 }
 
 /*
@@ -1174,7 +1199,7 @@ static int rcu_boost(struct rcu_node *rnp)
         t = container_of(tb, struct task_struct, rcu_node_entry);
         rt_mutex_init_proxy_locked(&mtx, t);
         t->rcu_boost_mutex = &mtx;
-        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
+        t->rcu_boosted = 1;
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
         rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
         rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
diff --git a/kernel/sched.c b/kernel/sched.c
index 14168c49a154..fde6ff903525 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2544,13 +2544,9 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
 }
 
 #ifdef CONFIG_SMP
-static void sched_ttwu_pending(void)
+static void sched_ttwu_do_pending(struct task_struct *list)
 {
         struct rq *rq = this_rq();
-        struct task_struct *list = xchg(&rq->wake_list, NULL);
-
-        if (!list)
-                return;
 
         raw_spin_lock(&rq->lock);
 
@@ -2563,9 +2559,45 @@ static void sched_ttwu_pending(void)
         raw_spin_unlock(&rq->lock);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void sched_ttwu_pending(void)
+{
+        struct rq *rq = this_rq();
+        struct task_struct *list = xchg(&rq->wake_list, NULL);
+
+        if (!list)
+                return;
+
+        sched_ttwu_do_pending(list);
+}
+
+#endif /* CONFIG_HOTPLUG_CPU */
+
 void scheduler_ipi(void)
 {
-        sched_ttwu_pending();
+        struct rq *rq = this_rq();
+        struct task_struct *list = xchg(&rq->wake_list, NULL);
+
+        if (!list)
+                return;
+
+        /*
+         * Not all reschedule IPI handlers call irq_enter/irq_exit, since
+         * traditionally all their work was done from the interrupt return
+         * path. Now that we actually do some work, we need to make sure
+         * we do call them.
+         *
+         * Some archs already do call them, luckily irq_enter/exit nest
+         * properly.
+         *
+         * Arguably we should visit all archs and update all handlers,
+         * however a fair share of IPIs are still resched only so this would
+         * somewhat pessimize the simple resched case.
+         */
+        irq_enter();
+        sched_ttwu_do_pending(list);
+        irq_exit();
 }
 
 static void ttwu_queue_remote(struct task_struct *p, int cpu)
diff --git a/kernel/signal.c b/kernel/signal.c
index ff7678603328..415d85d6f6c6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1178,18 +1178,25 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
 {
         struct sighand_struct *sighand;
 
-        rcu_read_lock();
         for (;;) {
+                local_irq_save(*flags);
+                rcu_read_lock();
                 sighand = rcu_dereference(tsk->sighand);
-                if (unlikely(sighand == NULL))
+                if (unlikely(sighand == NULL)) {
+                        rcu_read_unlock();
+                        local_irq_restore(*flags);
                         break;
+                }
 
-                spin_lock_irqsave(&sighand->siglock, *flags);
-                if (likely(sighand == tsk->sighand))
+                spin_lock(&sighand->siglock);
+                if (likely(sighand == tsk->sighand)) {
+                        rcu_read_unlock();
                         break;
-                spin_unlock_irqrestore(&sighand->siglock, *flags);
+                }
+                spin_unlock(&sighand->siglock);
+                rcu_read_unlock();
+                local_irq_restore(*flags);
         }
-        rcu_read_unlock();
 
         return sighand;
 }
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 40cf63ddd4b3..fca82c32042b 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -315,16 +315,24 @@ static inline void invoke_softirq(void)
 {
         if (!force_irqthreads)
                 __do_softirq();
-        else
+        else {
+                __local_bh_disable((unsigned long)__builtin_return_address(0),
+                                SOFTIRQ_OFFSET);
                 wakeup_softirqd();
+                __local_bh_enable(SOFTIRQ_OFFSET);
+        }
 }
 #else
 static inline void invoke_softirq(void)
 {
         if (!force_irqthreads)
                 do_softirq();
-        else
+        else {
+                __local_bh_disable((unsigned long)__builtin_return_address(0),
+                                SOFTIRQ_OFFSET);
                 wakeup_softirqd();
+                __local_bh_enable(SOFTIRQ_OFFSET);
+        }
 }
 #endif