In the C language, signed overflow is undefined. It is true that
twos-complement arithmetic normally comes to the rescue, but if the
compiler can subvert this any time it has any information about the values
being compared. For example, given "if (a - b > 0)", if the compiler
has enough information to realize that (for example) the value of "a"
is positive and that of "b" is negative, the compiler is within its
rights to optimize to a simple "if (1)", which might not be what you want.
This commit therefore converts synchronize_rcu_expedited()'s work-done
detection counter from signed to unsigned.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
EXPORT_SYMBOL_GPL(synchronize_rcu);
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
EXPORT_SYMBOL_GPL(synchronize_rcu);
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
-static long sync_rcu_preempt_exp_count;
+static unsigned long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
/*
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
/*
unsigned long flags;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_preempt_state;
unsigned long flags;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_preempt_state;
int trycount = 0;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
int trycount = 0;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
synchronize_rcu();
return;
}
synchronize_rcu();
return;
}
- if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
+ if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count)))
goto mb_ret; /* Others did our work for us. */
}
goto mb_ret; /* Others did our work for us. */
}
- if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
+ if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count)))
goto unlock_mb_ret; /* Others did our work for us. */
/* force all RCU readers onto ->blkd_tasks lists. */
goto unlock_mb_ret; /* Others did our work for us. */
/* force all RCU readers onto ->blkd_tasks lists. */