Remove argument from open_softirq which is always NULL
[linux-2.6.git] / kernel / rcupreempt.c
index 987cfb7..9dd827d 100644 (file)
  *             to Suparna Bhattacharya for pushing me completely away
  *             from atomic instructions on the read side.
  *
+ *  - Added handling of Dynamic Ticks
+ *      Copyright 2007 - Paul E. Mckenney <paulmck@us.ibm.com>
+ *                     - Steven Rostedt <srostedt@redhat.com>
+ *
  * Papers:  http://www.rdrop.com/users/paulmck/RCU
  *
  * Design Document: http://lwn.net/Articles/253651/
@@ -409,6 +413,212 @@ static void __rcu_advance_callbacks(struct rcu_data *rdp)
        }
 }
 
+#ifdef CONFIG_NO_HZ
+
+DEFINE_PER_CPU(long, dynticks_progress_counter) = 1;
+static DEFINE_PER_CPU(long, rcu_dyntick_snapshot);
+static DEFINE_PER_CPU(int, rcu_update_flag);
+
+/**
+ * rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
+ *
+ * If the CPU was idle with dynamic ticks active, this updates the
+ * dynticks_progress_counter to let the RCU handling know that the
+ * CPU is active.
+ */
+void rcu_irq_enter(void)
+{
+       int cpu = smp_processor_id();
+
+       if (per_cpu(rcu_update_flag, cpu))
+               per_cpu(rcu_update_flag, cpu)++;
+
+       /*
+        * Only update if we are coming from a stopped ticks mode
+        * (dynticks_progress_counter is even).
+        */
+       if (!in_interrupt() &&
+           (per_cpu(dynticks_progress_counter, cpu) & 0x1) == 0) {
+               /*
+                * The following might seem like we could have a race
+                * with NMI/SMIs. But this really isn't a problem.
+                * Here we do a read/modify/write, and the race happens
+                * when an NMI/SMI comes in after the read and before
+                * the write. But NMI/SMIs will increment this counter
+                * twice before returning, so the zero bit will not
+                * be corrupted by the NMI/SMI which is the most important
+                * part.
+                *
+                * The only thing is that we would bring back the counter
+                * to a postion that it was in during the NMI/SMI.
+                * But the zero bit would be set, so the rest of the
+                * counter would again be ignored.
+                *
+                * On return from the IRQ, the counter may have the zero
+                * bit be 0 and the counter the same as the return from
+                * the NMI/SMI. If the state machine was so unlucky to
+                * see that, it still doesn't matter, since all
+                * RCU read-side critical sections on this CPU would
+                * have already completed.
+                */
+               per_cpu(dynticks_progress_counter, cpu)++;
+               /*
+                * The following memory barrier ensures that any
+                * rcu_read_lock() primitives in the irq handler
+                * are seen by other CPUs to follow the above
+                * increment to dynticks_progress_counter. This is
+                * required in order for other CPUs to correctly
+                * determine when it is safe to advance the RCU
+                * grace-period state machine.
+                */
+               smp_mb(); /* see above block comment. */
+               /*
+                * Since we can't determine the dynamic tick mode from
+                * the dynticks_progress_counter after this routine,
+                * we use a second flag to acknowledge that we came
+                * from an idle state with ticks stopped.
+                */
+               per_cpu(rcu_update_flag, cpu)++;
+               /*
+                * If we take an NMI/SMI now, they will also increment
+                * the rcu_update_flag, and will not update the
+                * dynticks_progress_counter on exit. That is for
+                * this IRQ to do.
+                */
+       }
+}
+
+/**
+ * rcu_irq_exit - Called from exiting Hard irq context.
+ *
+ * If the CPU was idle with dynamic ticks active, update the
+ * dynticks_progress_counter to put let the RCU handling be
+ * aware that the CPU is going back to idle with no ticks.
+ */
+void rcu_irq_exit(void)
+{
+       int cpu = smp_processor_id();
+
+       /*
+        * rcu_update_flag is set if we interrupted the CPU
+        * when it was idle with ticks stopped.
+        * Once this occurs, we keep track of interrupt nesting
+        * because a NMI/SMI could also come in, and we still
+        * only want the IRQ that started the increment of the
+        * dynticks_progress_counter to be the one that modifies
+        * it on exit.
+        */
+       if (per_cpu(rcu_update_flag, cpu)) {
+               if (--per_cpu(rcu_update_flag, cpu))
+                       return;
+
+               /* This must match the interrupt nesting */
+               WARN_ON(in_interrupt());
+
+               /*
+                * If an NMI/SMI happens now we are still
+                * protected by the dynticks_progress_counter being odd.
+                */
+
+               /*
+                * The following memory barrier ensures that any
+                * rcu_read_unlock() primitives in the irq handler
+                * are seen by other CPUs to preceed the following
+                * increment to dynticks_progress_counter. This
+                * is required in order for other CPUs to determine
+                * when it is safe to advance the RCU grace-period
+                * state machine.
+                */
+               smp_mb(); /* see above block comment. */
+               per_cpu(dynticks_progress_counter, cpu)++;
+               WARN_ON(per_cpu(dynticks_progress_counter, cpu) & 0x1);
+       }
+}
+
+static void dyntick_save_progress_counter(int cpu)
+{
+       per_cpu(rcu_dyntick_snapshot, cpu) =
+               per_cpu(dynticks_progress_counter, cpu);
+}
+
+static inline int
+rcu_try_flip_waitack_needed(int cpu)
+{
+       long curr;
+       long snap;
+
+       curr = per_cpu(dynticks_progress_counter, cpu);
+       snap = per_cpu(rcu_dyntick_snapshot, cpu);
+       smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
+
+       /*
+        * If the CPU remained in dynticks mode for the entire time
+        * and didn't take any interrupts, NMIs, SMIs, or whatever,
+        * then it cannot be in the middle of an rcu_read_lock(), so
+        * the next rcu_read_lock() it executes must use the new value
+        * of the counter.  So we can safely pretend that this CPU
+        * already acknowledged the counter.
+        */
+
+       if ((curr == snap) && ((curr & 0x1) == 0))
+               return 0;
+
+       /*
+        * If the CPU passed through or entered a dynticks idle phase with
+        * no active irq handlers, then, as above, we can safely pretend
+        * that this CPU already acknowledged the counter.
+        */
+
+       if ((curr - snap) > 2 || (snap & 0x1) == 0)
+               return 0;
+
+       /* We need this CPU to explicitly acknowledge the counter flip. */
+
+       return 1;
+}
+
+static inline int
+rcu_try_flip_waitmb_needed(int cpu)
+{
+       long curr;
+       long snap;
+
+       curr = per_cpu(dynticks_progress_counter, cpu);
+       snap = per_cpu(rcu_dyntick_snapshot, cpu);
+       smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
+
+       /*
+        * If the CPU remained in dynticks mode for the entire time
+        * and didn't take any interrupts, NMIs, SMIs, or whatever,
+        * then it cannot have executed an RCU read-side critical section
+        * during that time, so there is no need for it to execute a
+        * memory barrier.
+        */
+
+       if ((curr == snap) && ((curr & 0x1) == 0))
+               return 0;
+
+       /*
+        * If the CPU either entered or exited an outermost interrupt,
+        * SMI, NMI, or whatever handler, then we know that it executed
+        * a memory barrier when doing so.  So we don't need another one.
+        */
+       if (curr != snap)
+               return 0;
+
+       /* We need the CPU to execute a memory barrier. */
+
+       return 1;
+}
+
+#else /* !CONFIG_NO_HZ */
+
+# define dyntick_save_progress_counter(cpu)    do { } while (0)
+# define rcu_try_flip_waitack_needed(cpu)      (1)
+# define rcu_try_flip_waitmb_needed(cpu)       (1)
+
+#endif /* CONFIG_NO_HZ */
+
 /*
  * Get here when RCU is idle.  Decide whether we need to
  * move out of idle state, and return non-zero if so.
@@ -447,8 +657,10 @@ rcu_try_flip_idle(void)
 
        /* Now ask each CPU for acknowledgement of the flip. */
 
-       for_each_cpu_mask(cpu, rcu_cpu_online_map)
+       for_each_cpu_mask(cpu, rcu_cpu_online_map) {
                per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
+               dyntick_save_progress_counter(cpu);
+       }
 
        return 1;
 }
@@ -464,7 +676,8 @@ rcu_try_flip_waitack(void)
 
        RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
        for_each_cpu_mask(cpu, rcu_cpu_online_map)
-               if (per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
+               if (rcu_try_flip_waitack_needed(cpu) &&
+                   per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
                        RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
                        return 0;
                }
@@ -509,8 +722,10 @@ rcu_try_flip_waitzero(void)
        smp_mb();  /*  ^^^^^^^^^^^^ */
 
        /* Call for a memory barrier from each CPU. */
-       for_each_cpu_mask(cpu, rcu_cpu_online_map)
+       for_each_cpu_mask(cpu, rcu_cpu_online_map) {
                per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
+               dyntick_save_progress_counter(cpu);
+       }
 
        RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
        return 1;
@@ -528,7 +743,8 @@ rcu_try_flip_waitmb(void)
 
        RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
        for_each_cpu_mask(cpu, rcu_cpu_online_map)
-               if (per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
+               if (rcu_try_flip_waitmb_needed(cpu) &&
+                   per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
                        RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
                        return 0;
                }
@@ -702,8 +918,9 @@ void rcu_offline_cpu(int cpu)
         * fix.
         */
 
+       local_irq_save(flags);
        rdp = RCU_DATA_ME();
-       spin_lock_irqsave(&rdp->lock, flags);
+       spin_lock(&rdp->lock);
        *rdp->nexttail = list;
        if (list)
                rdp->nexttail = tail;
@@ -735,9 +952,11 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 {
        unsigned long flags;
        struct rcu_head *next, *list;
-       struct rcu_data *rdp = RCU_DATA_ME();
+       struct rcu_data *rdp;
 
-       spin_lock_irqsave(&rdp->lock, flags);
+       local_irq_save(flags);
+       rdp = RCU_DATA_ME();
+       spin_lock(&rdp->lock);
        list = rdp->donelist;
        if (list == NULL) {
                spin_unlock_irqrestore(&rdp->lock, flags);
@@ -788,10 +1007,10 @@ void __synchronize_sched(void)
        if (sched_getaffinity(0, &oldmask) < 0)
                oldmask = cpu_possible_map;
        for_each_online_cpu(cpu) {
-               sched_setaffinity(0, cpumask_of_cpu(cpu));
+               sched_setaffinity(0, &cpumask_of_cpu(cpu));
                schedule();
        }
-       sched_setaffinity(0, oldmask);
+       sched_setaffinity(0, &oldmask);
 }
 EXPORT_SYMBOL_GPL(__synchronize_sched);
 
@@ -906,7 +1125,7 @@ void __init __rcu_init(void)
        for_each_online_cpu(cpu)
                rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
 
-       open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
+       open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 }
 
 /*