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

* '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

diff --git a/include/linux/sched.h b/include/linux/sched.h
index bde99d5358dc84af2fceb2a20199bd9ed7556426..14a6c7b545de5bf3ad51dea50d5d484cfc8bfbb5 100644 (file)
--- 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 75113cb7c4fb251b60b77de84842b0b3ed787888..8aafbb80b8b093e1072f2fcc4dc66bf40f249b7f 100644 (file)
--- 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 14168c49a15428880f5b66702e12134eff4ba1fa..fde6ff90352583d65ff890a407200f2fb0c3073e 100644 (file)
--- 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 ff7678603328b3ba5e00c74dc9fd08bcbf113987..415d85d6f6c637b099826d012e46f70832b1d557 100644 (file)
--- 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 40cf63ddd4b3d740d2620ddbf1fa245830b1d703..fca82c32042b73133f2ab74838287c94cf8ad152 100644 (file)
--- 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