epoll: make epoll_wait() use the hrtimer range feature

This make epoll use hrtimers for the timeout value which prevents
epoll_wait() from timing out up to a millisecond early.

This mirrors the behavior of select() and poll().

Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 22 insertions, 17 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 256bb7bb102a..8cf07242067d 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -77,9 +77,6 @@
 /* Maximum number of nesting allowed inside epoll sets */
 #define EP_MAX_NESTS 4
 
-/* Maximum msec timeout value storeable in a long int */
-#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
-
 #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
 
 #define EP_UNACTIVE_PTR ((void *) -1L)
@@ -1117,18 +1114,22 @@ static int ep_send_events(struct eventpoll *ep,
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
                    int maxevents, long timeout)
 {
-        int res, eavail;
+        int res, eavail, timed_out = 0;
         unsigned long flags;
-        long jtimeout;
+        long slack;
         wait_queue_t wait;
-
-        /*
-         * Calculate the timeout by checking for the "infinite" value (-1)
-         * and the overflow condition. The passed timeout is in milliseconds,
-         * that why (t * HZ) / 1000.
-         */
-        jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
-                MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
+        struct timespec end_time;
+        ktime_t expires, *to = NULL;
+
+        if (timeout > 0) {
+                ktime_get_ts(&end_time);
+                timespec_add_ns(&end_time, (u64)timeout * NSEC_PER_MSEC);
+                slack = select_estimate_accuracy(&end_time);
+                to = &expires;
+                *to = timespec_to_ktime(end_time);
+        } else if (timeout == 0) {
+                timed_out = 1;
+        }
 
 retry:
         spin_lock_irqsave(&ep->lock, flags);
@@ -1150,7 +1151,7 @@ retry:
                          * to TASK_INTERRUPTIBLE before doing the checks.
                          */
                         set_current_state(TASK_INTERRUPTIBLE);
-                        if (!list_empty(&ep->rdllist) || !jtimeout)
+                        if (!list_empty(&ep->rdllist) || timed_out)
                                 break;
                         if (signal_pending(current)) {
                                 res = -EINTR;
@@ -1158,7 +1159,9 @@ retry:
                         }
 
                         spin_unlock_irqrestore(&ep->lock, flags);
-                        jtimeout = schedule_timeout(jtimeout);
+                        if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+                                timed_out = 1;
+
                         spin_lock_irqsave(&ep->lock, flags);
                 }
                 __remove_wait_queue(&ep->wq, &wait);
@@ -1176,7 +1179,7 @@ retry:
          * more luck.
          */
         if (!res && eavail &&
-            !(res = ep_send_events(ep, events, maxevents)) && jtimeout)
+            !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
                 goto retry;
 
         return res;
diff --git a/fs/select.c b/fs/select.c
index 5f023f911202..b7b10aa30861 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -67,7 +67,7 @@ static long __estimate_accuracy(struct timespec *tv)
         return slack;
 }
 
-static long select_estimate_accuracy(struct timespec *tv)
+long select_estimate_accuracy(struct timespec *tv)
 {
         unsigned long ret;
         struct timespec now;
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 600cc1fde64d..56e76af78102 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -73,6 +73,8 @@ extern void poll_initwait(struct poll_wqueues *pwq);
 extern void poll_freewait(struct poll_wqueues *pwq);
 extern int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
                                  ktime_t *expires, unsigned long slack);
+extern long select_estimate_accuracy(struct timespec *tv);
+
 
 static inline int poll_schedule(struct poll_wqueues *pwq, int state)
 {