[PATCH] preempt/hardirq.h: Clarify PREEMPT_ACTIVE bit location

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

By default, the PREEMPT_ACTIVE flag is bit 27, but different
architectures can override that. Update the comment to reflect
this fact.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 include/linux/hardirq.h |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 305f23c..483aa60 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -20,10 +20,15 @@
  * hardirq nesting. An arch may choose to give less than 10 bits.
  * m68k expects it to be 8.
  *
+ * By default, the bits are defined as shown below:
+ *
  * - bits 16-25 are the hardirq count (max # of nested hardirqs: 1024)
  * - bit 26 is the NMI_MASK
  * - bit 27 is the PREEMPT_ACTIVE flag
  *
+ * However, different architectures may override them. (For example,
+ * x86 defines bit 28 as the PREEMPT_ACTIVE flag).
+ *
  * PREEMPT_MASK: 0x000000ff
  * SOFTIRQ_MASK: 0x0000ff00
  * HARDIRQ_MASK: 0x03ff0000