1 files changed, 45 insertions, 6 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 79b557c63381..456c99054160 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1920,10 +1920,9 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
  * They are read and saved off onto struct rq in update_rq_clock().
  * This may result in other CPU reading this CPU's irq time and can
  * race with irq/account_system_vtime on this CPU. We would either get old
- * or new value (or semi updated value on 32 bit) with a side effect of
- * accounting a slice of irq time to wrong task when irq is in progress
- * while we read rq->clock. That is a worthy compromise in place of having
- * locks on each irq in account_system_time.
+ * or new value with a side effect of accounting a slice of irq time to wrong
+ * task when irq is in progress while we read rq->clock. That is a worthy
+ * compromise in place of having locks on each irq in account_system_time.
  */
 static DEFINE_PER_CPU(u64, cpu_hardirq_time);
 static DEFINE_PER_CPU(u64, cpu_softirq_time);
@@ -1941,10 +1940,48 @@ void disable_sched_clock_irqtime(void)
         sched_clock_irqtime = 0;
 }
 
-static inline u64 irq_time_cpu(int cpu)
+#ifndef CONFIG_64BIT
+static DEFINE_PER_CPU(seqcount_t, irq_time_seq);
+
+static inline void irq_time_write_begin(void)
+{
+        __this_cpu_inc(irq_time_seq.sequence);
+        smp_wmb();
+}
+
+static inline void irq_time_write_end(void)
+{
+        smp_wmb();
+        __this_cpu_inc(irq_time_seq.sequence);
+}
+
+static inline u64 irq_time_read(int cpu)
+{
+        u64 irq_time;
+        unsigned seq;
+
+        do {
+                seq = read_seqcount_begin(&per_cpu(irq_time_seq, cpu));
+                irq_time = per_cpu(cpu_softirq_time, cpu) +
+                           per_cpu(cpu_hardirq_time, cpu);
+        } while (read_seqcount_retry(&per_cpu(irq_time_seq, cpu), seq));
+
+        return irq_time;
+}
+#else /* CONFIG_64BIT */
+static inline void irq_time_write_begin(void)
+{
+}
+
+static inline void irq_time_write_end(void)
+{
+}
+
+static inline u64 irq_time_read(int cpu)
 {
         return per_cpu(cpu_softirq_time, cpu) + per_cpu(cpu_hardirq_time, cpu);
 }
+#endif /* CONFIG_64BIT */
 
 /*
  * Called before incrementing preempt_count on {soft,}irq_enter
@@ -1965,6 +2002,7 @@ void account_system_vtime(struct task_struct *curr)
         delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time);
         __this_cpu_add(irq_start_time, delta);
 
+        irq_time_write_begin();
         /*
          * We do not account for softirq time from ksoftirqd here.
          * We want to continue accounting softirq time to ksoftirqd thread
@@ -1976,6 +2014,7 @@ void account_system_vtime(struct task_struct *curr)
         else if (in_serving_softirq() && !(curr->flags & PF_KSOFTIRQD))
                 __this_cpu_add(cpu_softirq_time, delta);
 
+        irq_time_write_end();
         local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(account_system_vtime);
@@ -1984,7 +2023,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 {
         s64 irq_delta;
 
-        irq_delta = irq_time_cpu(cpu_of(rq)) - rq->prev_irq_time;
+        irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
 
         /*
          * Since irq_time is only updated on {soft,}irq_exit, we might run into