rcu: Stop overflowing signed integers

The C standard does not specify the result of an operation that
overflows a signed integer, so such operations need to be
avoided.  This patch changes the type of several fields from
"long" to "unsigned long" and adjusts operations as needed.
ULONG_CMP_GE() and ULONG_CMP_LT() macros are introduced to do
the modular comparisons that are appropriate given that overflow
is an expected event.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-17-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 18 insertions, 15 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index d9d032abd665..7495fed49c30 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -92,10 +92,10 @@ struct rcu_dynticks {
 struct rcu_node {
         spinlock_t lock;        /* Root rcu_node's lock protects some */
                                 /*  rcu_state fields as well as following. */
-        long    gpnum;          /* Current grace period for this node. */
+        unsigned long gpnum;    /* Current grace period for this node. */
                                 /*  This will either be equal to or one */
                                 /*  behind the root rcu_node's gpnum. */
-        long    completed;      /* Last grace period completed for this node. */
+        unsigned long completed; /* Last GP completed for this node. */
                                 /*  This will either be equal to or one */
                                 /*  behind the root rcu_node's gpnum. */
         unsigned long qsmask;   /* CPUs or groups that need to switch in */
@@ -161,11 +161,11 @@ struct rcu_node {
 /* Per-CPU data for read-copy update. */
 struct rcu_data {
         /* 1) quiescent-state and grace-period handling : */
-        long            completed;      /* Track rsp->completed gp number */
+        unsigned long   completed;      /* Track rsp->completed gp number */
                                         /*  in order to detect GP end. */
-        long            gpnum;          /* Highest gp number that this CPU */
+        unsigned long   gpnum;          /* Highest gp number that this CPU */
                                         /*  is aware of having started. */
-        long            passed_quiesc_completed;
+        unsigned long   passed_quiesc_completed;
                                         /* Value of completed at time of qs. */
         bool            passed_quiesc;  /* User-mode/idle loop etc. */
         bool            qs_pending;     /* Core waits for quiesc state. */
@@ -221,14 +221,14 @@ struct rcu_data {
         unsigned long resched_ipi;      /* Sent a resched IPI. */
 
         /* 5) __rcu_pending() statistics. */
-        long n_rcu_pending;             /* rcu_pending() calls since boot. */
-        long n_rp_qs_pending;
-        long n_rp_cb_ready;
-        long n_rp_cpu_needs_gp;
-        long n_rp_gp_completed;
-        long n_rp_gp_started;
-        long n_rp_need_fqs;
-        long n_rp_need_nothing;
+        unsigned long n_rcu_pending;    /* rcu_pending() calls since boot. */
+        unsigned long n_rp_qs_pending;
+        unsigned long n_rp_cb_ready;
+        unsigned long n_rp_cpu_needs_gp;
+        unsigned long n_rp_gp_completed;
+        unsigned long n_rp_gp_started;
+        unsigned long n_rp_need_fqs;
+        unsigned long n_rp_need_nothing;
 
         int cpu;
 };
@@ -255,6 +255,9 @@ struct rcu_data {
 
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
+#define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
+#define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
+
 /*
  * RCU global state, including node hierarchy.  This hierarchy is
  * represented in "heap" form in a dense array.  The root (first level)
@@ -283,8 +286,8 @@ struct rcu_state {
                                                 /*  period because */
                                                 /*  force_quiescent_state() */
                                                 /*  was running. */
-        long    gpnum;                          /* Current gp number. */
-        long    completed;                      /* # of last completed gp. */
+        unsigned long gpnum;                    /* Current gp number. */
+        unsigned long completed;                /* # of last completed gp. */
 
         /* End of fields guarded by root rcu_node's lock. */