epoll: epoll_wait() should not use timespec_add_ns()

commit 95aac7b1cd224f ("epoll: make epoll_wait() use the hrtimer range
feature") added a performance regression because it uses timespec_add_ns()
with potential very large 'ns' values.

[akpm@linux-foundation.org: s/epoll_set_mstimeout/ep_set_mstimeout/, per Davide]
Reported-by: Simon Kirby <sim@hostway.ca>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>		[2.6.37.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index cc8a9b7d606494d5b556927808feeba29f858d45..267d0ada45414a6f9cd8e90efeb9714e52e65de9 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1114,6 +1114,17 @@ static int ep_send_events(struct eventpoll *ep,
        return ep_scan_ready_list(ep, ep_send_events_proc, &esed);
 }
 
+static inline struct timespec ep_set_mstimeout(long ms)
+{
+       struct timespec now, ts = {
+               .tv_sec = ms / MSEC_PER_SEC,
+               .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
+       };
+
+       ktime_get_ts(&now);
+       return timespec_add_safe(now, ts);
+}
+
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
                   int maxevents, long timeout)
 {
@@ -1121,12 +1132,11 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
        unsigned long flags;
        long slack;
        wait_queue_t wait;
-       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);
+               struct timespec end_time = ep_set_mstimeout(timeout);
+
                slack = select_estimate_accuracy(&end_time);
                to = &expires;
                *to = timespec_to_ktime(end_time);