hrtimer: fix signed/unsigned bug in slack estimator

the slack estimator used unsigned math; however for very short delay it's
possible that by the time you calculate the timeout, it's already passed and
you get a negative time/slack... in an unsigned variable... which then gets
turned into a 100 msec delay rather than zero.

This patch fixes this by using a signed typee in the right places.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

diff --git a/fs/select.c b/fs/select.c
index fdd8584e536dca956dd1b8a6ec4c68f2ef8ea9f5..448e44001286754f891249f216f7af3a01d1bfee 100644 (file)
--- a/fs/select.c
+++ b/fs/select.c
@@ -41,9 +41,9 @@
  * better solutions..
  */
 
-static unsigned long __estimate_accuracy(struct timespec *tv)
+static long __estimate_accuracy(struct timespec *tv)
 {
-       unsigned long slack;
+       long slack;
        int divfactor = 1000;
 
        if (task_nice(current) > 0)
@@ -54,10 +54,13 @@ static unsigned long __estimate_accuracy(struct timespec *tv)
 
        if (slack > 100 * NSEC_PER_MSEC)
                slack =  100 * NSEC_PER_MSEC;
+
+       if (slack < 0)
+               slack = 0;
        return slack;
 }
 
-static unsigned long estimate_accuracy(struct timespec *tv)
+static long estimate_accuracy(struct timespec *tv)
 {
        unsigned long ret;
        struct timespec now;
@@ -330,7 +333,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
                timed_out = 1;
        }
 
-       if (end_time)
+       if (end_time && !timed_out)
                slack = estimate_accuracy(end_time);
 
        retval = 0;
@@ -656,7 +659,7 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
                timed_out = 1;
        }
 
-       if (end_time)
+       if (end_time && !timed_out)
                slack = estimate_accuracy(end_time);
 
        for (;;) {