net: convert lls to use time_in_range()

Time in range will fail safely if we move to a different cpu with an
extremely large clock skew.
Add time_in_range64() and convert lls to use it.

changelog:
v2
- fixed double call to sched_clock in can_poll_ll
- fixed checkpatchisms
Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/select.c

@@ -403,7 +403,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
 	int retval, i, timed_out = 0;
 	unsigned long slack = 0;
 	unsigned int ll_flag = ll_get_flag();
-	u64 ll_time = ll_end_time();
+	u64 ll_start = ll_start_time(ll_flag);
+	u64 ll_time = ll_run_time();
 
 	rcu_read_lock();
 	retval = max_select_fd(n, fds);
@@ -498,7 +499,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
 		}
 
 		/* only if on, have sockets with POLL_LL and not out of time */
-		if (ll_flag && can_ll && can_poll_ll(ll_time))
+		if (ll_flag && can_ll && can_poll_ll(ll_start, ll_time))
 			continue;
 
 		/*
@@ -770,7 +771,8 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
 	int timed_out = 0, count = 0;
 	unsigned long slack = 0;
 	unsigned int ll_flag = ll_get_flag();
-	u64 ll_time = ll_end_time();
+	u64 ll_start = ll_start_time(ll_flag);
+	u64 ll_time = ll_run_time();
 
 	/* Optimise the no-wait case */
 	if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
@@ -819,7 +821,7 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
 			break;
 
 		/* only if on, have sockets with POLL_LL and not out of time */
-		if (ll_flag && can_ll && can_poll_ll(ll_time))
+		if (ll_flag && can_ll && can_poll_ll(ll_start, ll_time))
 			continue;
 
 		/*

include/linux/jiffies.h

@@ -139,6 +139,10 @@ static inline u64 get_jiffies_64(void)
 	 ((__s64)(a) - (__s64)(b) >= 0))
 #define time_before_eq64(a,b)	time_after_eq64(b,a)
 
+#define time_in_range64(a, b, c) \
+	(time_after_eq64(a, b) && \
+	 time_before_eq64(a, c))
+
 /*
  * These four macros compare jiffies and 'a' for convenience.
  */

include/net/ll_poll.h

@@ -67,19 +67,23 @@ static inline u64 ll_sched_clock(void)
 /* we don't mind a ~2.5% imprecision so <<10 instead of *1000
  * sk->sk_ll_usec is a u_int so this can't overflow
  */
-static inline u64 ll_sk_end_time(struct sock *sk)
+static inline u64 ll_sk_run_time(struct sock *sk)
 {
-	return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + ll_sched_clock();
+	return (u64)ACCESS_ONCE(sk->sk_ll_usec) << 10;
 }
 
 /* in poll/select we use the global sysctl_net_ll_poll value
  * only call sched_clock() if enabled
  */
-static inline u64 ll_end_time(void)
+static inline u64 ll_run_time(void)
 {
-	u64 end_time = ACCESS_ONCE(sysctl_net_ll_poll);
+	return (u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10;
+}
 
-	return end_time ? (end_time << 10) + ll_sched_clock() : 0;
+/* if flag is not set we don't need to know the time */
+static inline u64 ll_start_time(unsigned int flag)
+{
+	return flag ? ll_sched_clock() : 0;
 }
 
 static inline bool sk_valid_ll(struct sock *sk)
@@ -88,9 +92,12 @@ static inline bool sk_valid_ll(struct sock *sk)
 	       !need_resched() && !signal_pending(current);
 }
 
-static inline bool can_poll_ll(u64 end_time)
+/* careful! time_in_range64 will evaluate now twice */
+static inline bool can_poll_ll(u64 start_time, u64 run_time)
 {
-	return !time_after64(ll_sched_clock(), end_time);
+	u64 now = ll_sched_clock();
+
+	return time_in_range64(now, start_time, start_time + run_time);
 }
 
 /* when used in sock_poll() nonblock is known at compile time to be true
@@ -98,7 +105,8 @@ static inline bool can_poll_ll(u64 end_time)
  */
 static inline bool sk_poll_ll(struct sock *sk, int nonblock)
 {
-	u64 end_time = nonblock ? 0 : ll_sk_end_time(sk);
+	u64 start_time = ll_start_time(!nonblock);
+	u64 run_time = ll_sk_run_time(sk);
 	const struct net_device_ops *ops;
 	struct napi_struct *napi;
 	int rc = false;
@@ -129,7 +137,7 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock)
 					 LINUX_MIB_LOWLATENCYRXPACKETS, rc);
 
 	} while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
-		 can_poll_ll(end_time));
+		 can_poll_ll(start_time, run_time));
 
 	rc = !skb_queue_empty(&sk->sk_receive_queue);
 out: