2 files changed, 16 insertions, 6 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ab95fef38d56..f562674db404 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -68,9 +68,15 @@ enum {
         WORK_STRUCT_FLAG_BITS   = WORK_STRUCT_COLOR_SHIFT +
                                   WORK_STRUCT_COLOR_BITS,
 
+        /* data contains off-queue information when !WORK_STRUCT_CWQ */
+        WORK_OFFQ_FLAG_BASE     = WORK_STRUCT_FLAG_BITS,
+        WORK_OFFQ_FLAG_BITS     = 0,
+        WORK_OFFQ_CPU_SHIFT     = WORK_OFFQ_FLAG_BASE + WORK_OFFQ_FLAG_BITS,
+
+        /* convenience constants */
         WORK_STRUCT_FLAG_MASK   = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
         WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
-        WORK_STRUCT_NO_CPU      = WORK_CPU_NONE << WORK_STRUCT_FLAG_BITS,
+        WORK_STRUCT_NO_CPU      = (unsigned long)WORK_CPU_NONE << WORK_OFFQ_CPU_SHIFT,
 
         /* bit mask for work_busy() return values */
         WORK_BUSY_PENDING       = 1 << 0,
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0f50f4078e36..eeae77079483 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -533,9 +533,9 @@ static int work_next_color(int color)
 }
 
 /*
- * A work's data points to the cwq with WORK_STRUCT_CWQ set while the
- * work is on queue.  Once execution starts, WORK_STRUCT_CWQ is
- * cleared and the work data contains the cpu number it was last on.
+ * While queued, %WORK_STRUCT_CWQ is set and non flag bits of a work's data
+ * contain the pointer to the queued cwq.  Once execution starts, the flag
+ * is cleared and the high bits contain OFFQ flags and CPU number.
  *
  * set_work_cwq(), set_work_cpu_and_clear_pending() and clear_work_data()
  * can be used to set the cwq, cpu or clear work->data.  These functions
@@ -565,7 +565,7 @@ static void set_work_cwq(struct work_struct *work,
 static void set_work_cpu_and_clear_pending(struct work_struct *work,
                                            unsigned int cpu)
 {
-        set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, 0);
+        set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0);
 }
 
 static void clear_work_data(struct work_struct *work)
@@ -592,7 +592,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
                 return ((struct cpu_workqueue_struct *)
                         (data & WORK_STRUCT_WQ_DATA_MASK))->pool->gcwq;
 
-        cpu = data >> WORK_STRUCT_FLAG_BITS;
+        cpu = data >> WORK_OFFQ_CPU_SHIFT;
         if (cpu == WORK_CPU_NONE)
                 return NULL;
 
@@ -3724,6 +3724,10 @@ static int __init init_workqueues(void)
         unsigned int cpu;
         int i;
 
+        /* make sure we have enough bits for OFFQ CPU number */
+        BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_CPU_SHIFT)) <
+                     WORK_CPU_LAST);
+
         cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
         cpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);