[PATCH tip/core/rcu 2/5] srcu: Prevent sdp->srcu_gp_seq_needed_exp counter wrap

[Paul E. McKenney]

From: Ildar Ismagilov <devi...@gmail.com>

SRCU checks each srcu_data structure's grace-period number for counter
wrap four times per cycle by default.  This frequency guarantees that
normal comparisons will detect potential wrap.  However, the expedited
grace-period number is not checked.  The consquences are not too horrible
(a failure to expedite a grace period when requested), but it would be
good to avoid such things.  This commit therefore adds this check to
the expedited grace-period number.

Signed-off-by: Ildar Ismagilov <devi...@gmail.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
 kernel/rcu/srcutree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 01f4a8bf0e03..bb9607baad9b 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -579,6 +579,9 @@ static void srcu_gp_end(struct srcu_struct *sp)
                                if (ULONG_CMP_GE(gpseq,
                                                 sdp->srcu_gp_seq_needed + 100))
                                        sdp->srcu_gp_seq_needed = gpseq;
+                               if (ULONG_CMP_GE(gpseq,
+                                                sdp->srcu_gp_seq_needed_exp + 
100))
+                                       sdp->srcu_gp_seq_needed_exp = gpseq;
                                spin_unlock_irqrestore_rcu_node(sdp, flags);
                        }
        }
-- 
2.5.2