generic-ipi: remove CSD_FLAG_WAIT

Oleg noticed that we don't strictly need CSD_FLAG_WAIT, rework
the code so that we can use CSD_FLAG_LOCK for both purposes.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

5 files changed, 28 insertions, 71 deletions

diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index ce0efc6b26dc..ee9c21602228 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -64,7 +64,7 @@ static int raise_blk_irq(int cpu, struct request *rq)
                 data->info = rq;
                 data->flags = 0;
 
-                __smp_call_function_single(cpu, data);
+                __smp_call_function_single(cpu, data, 0);
                 return 0;
         }
 
diff --git a/include/linux/smp.h b/include/linux/smp.h
index 715196b09d67..00866d7fdf34 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -82,7 +82,8 @@ smp_call_function_mask(cpumask_t mask, void(*func)(void *info), void *info,
         return 0;
 }
 
-void __smp_call_function_single(int cpuid, struct call_single_data *data);
+void __smp_call_function_single(int cpuid, struct call_single_data *data,
+                                int wait);
 
 /*
  * Generic and arch helpers
diff --git a/kernel/sched.c b/kernel/sched.c
index 410eec404133..d4c2749a2998 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1093,7 +1093,7 @@ static void hrtick_start(struct rq *rq, u64 delay)
         if (rq == this_rq()) {
                 hrtimer_restart(timer);
         } else if (!rq->hrtick_csd_pending) {
-                __smp_call_function_single(cpu_of(rq), &rq->hrtick_csd);
+                __smp_call_function_single(cpu_of(rq), &rq->hrtick_csd, 0);
                 rq->hrtick_csd_pending = 1;
         }
 }
diff --git a/kernel/smp.c b/kernel/smp.c
index 7a0ce25829dc..f5308258891a 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -23,8 +23,7 @@ static struct {
 };
 
 enum {
-        CSD_FLAG_WAIT           = 0x01,
-        CSD_FLAG_LOCK           = 0x02,
+        CSD_FLAG_LOCK           = 0x01,
 };
 
 struct call_function_data {
@@ -95,41 +94,21 @@ static int __cpuinit init_call_single_data(void)
 early_initcall(init_call_single_data);
 
 /*
- * csd_wait/csd_complete are used for synchronous ipi calls
- */
-static void csd_wait_prepare(struct call_single_data *data)
-{
-        data->flags |= CSD_FLAG_WAIT;
-}
-
-static void csd_complete(struct call_single_data *data)
-{
-        if (data->flags & CSD_FLAG_WAIT) {
-                /*
-                 * ensure we're all done before saying we are
-                 */
-                smp_mb();
-                data->flags &= ~CSD_FLAG_WAIT;
-        }
-}
-
-static void csd_wait(struct call_single_data *data)
-{
-        while (data->flags & CSD_FLAG_WAIT)
-                cpu_relax();
-}
-
-/*
  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
  *
  * For non-synchronous ipi calls the csd can still be in use by the previous
  * function call. For multi-cpu calls its even more interesting as we'll have
  * to ensure no other cpu is observing our csd.
  */
-static void csd_lock(struct call_single_data *data)
+static void csd_lock_wait(struct call_single_data *data)
 {
         while (data->flags & CSD_FLAG_LOCK)
                 cpu_relax();
+}
+
+static void csd_lock(struct call_single_data *data)
+{
+        csd_lock_wait(data);
         data->flags = CSD_FLAG_LOCK;
 
         /*
@@ -155,11 +134,12 @@ static void csd_unlock(struct call_single_data *data)
  * Insert a previously allocated call_single_data element for execution
  * on the given CPU. data must already have ->func, ->info, and ->flags set.
  */
-static void generic_exec_single(int cpu, struct call_single_data *data)
+static
+void generic_exec_single(int cpu, struct call_single_data *data, int wait)
 {
         struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
-        int wait = data->flags & CSD_FLAG_WAIT, ipi;
         unsigned long flags;
+        int ipi;
 
         spin_lock_irqsave(&dst->lock, flags);
         ipi = list_empty(&dst->list);
@@ -182,7 +162,7 @@ static void generic_exec_single(int cpu, struct call_single_data *data)
                 arch_send_call_function_single_ipi(cpu);
 
         if (wait)
-                csd_wait(data);
+                csd_lock_wait(data);
 }
 
 /*
@@ -232,7 +212,6 @@ void generic_smp_call_function_interrupt(void)
                 if (refs)
                         continue;
 
-                csd_complete(&data->csd);
                 csd_unlock(&data->csd);
         }
 
@@ -270,9 +249,6 @@ void generic_smp_call_function_single_interrupt(void)
 
                 data->func(data->info);
 
-                if (data_flags & CSD_FLAG_WAIT)
-                        csd_complete(data);
-
                 /*
                  * Unlocked CSDs are valid through generic_exec_single()
                  */
@@ -313,36 +289,16 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
                 func(info);
                 local_irq_restore(flags);
         } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
-                struct call_single_data *data;
+                struct call_single_data *data = &d;
 
-                if (!wait) {
-                        /*
-                         * We are calling a function on a single CPU
-                         * and we are not going to wait for it to finish.
-                         * We use a per cpu data to pass the information to
-                         * that CPU. Since all callers of this code will
-                         * use the same data, we must synchronize the
-                         * callers to prevent a new caller from corrupting
-                         * the data before the callee can access it.
-                         *
-                         * The CSD_FLAG_LOCK is used to let us know when
-                         * the IPI handler is done with the data.
-                         * The first caller will set it, and the callee
-                         * will clear it. The next caller must wait for
-                         * it to clear before we set it again. This
-                         * will make sure the callee is done with the
-                         * data before a new caller will use it.
-                         */
+                if (!wait)
                         data = &__get_cpu_var(csd_data);
-                        csd_lock(data);
-                } else {
-                        data = &d;
-                        csd_wait_prepare(data);
-                }
+
+                csd_lock(data);
 
                 data->func = func;
                 data->info = info;
-                generic_exec_single(cpu, data);
+                generic_exec_single(cpu, data, wait);
         } else {
                 err = -ENXIO;   /* CPU not online */
         }
@@ -362,12 +318,15 @@ EXPORT_SYMBOL(smp_call_function_single);
  * instance.
  *
  */
-void __smp_call_function_single(int cpu, struct call_single_data *data)
+void __smp_call_function_single(int cpu, struct call_single_data *data,
+                                int wait)
 {
+        csd_lock(data);
+
         /* Can deadlock when called with interrupts disabled */
-        WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
+        WARN_ON(wait && irqs_disabled());
 
-        generic_exec_single(cpu, data);
+        generic_exec_single(cpu, data, wait);
 }
 
 /* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
@@ -425,9 +384,6 @@ void smp_call_function_many(const struct cpumask *mask,
         csd_lock(&data->csd);
 
         spin_lock_irqsave(&data->lock, flags);
-        if (wait)
-                csd_wait_prepare(&data->csd);
-
         data->csd.func = func;
         data->csd.info = info;
         cpumask_and(data->cpumask, mask, cpu_online_mask);
@@ -456,7 +412,7 @@ void smp_call_function_many(const struct cpumask *mask,
 
         /* optionally wait for the CPUs to complete */
         if (wait)
-                csd_wait(&data->csd);
+                csd_lock_wait(&data->csd);
 }
 EXPORT_SYMBOL(smp_call_function_many);
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index bdbe9de9cd8d..48c3d5d627a8 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -496,7 +496,7 @@ static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softir
                 cp->flags = 0;
                 cp->priv = softirq;
 
-                __smp_call_function_single(cpu, cp);
+                __smp_call_function_single(cpu, cp, 0);
                 return 0;
         }
         return 1;