1 files changed, 16 insertions, 21 deletions

diff --git a/kernel/itimer.c b/kernel/itimer.c
index a72cb0e5aa4b..7c1b25e25e47 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -112,28 +112,11 @@ asmlinkage long sys_getitimer(int which, struct itimerval __user *value)
         return error;
 }
 
-/*
- * Called with P->sighand->siglock held and P->signal->real_timer inactive.
- * If interval is nonzero, arm the timer for interval ticks from now.
- */
-static inline void it_real_arm(struct task_struct *p, unsigned long interval)
-{
-        p->signal->it_real_value = interval; /* XXX unnecessary field?? */
-        if (interval == 0)
-                return;
-        if (interval > (unsigned long) LONG_MAX)
-                interval = LONG_MAX;
-        /* the "+ 1" below makes sure that the timer doesn't go off before
-         * the interval requested. This could happen if
-         * time requested % (usecs per jiffy) is more than the usecs left
-         * in the current jiffy */
-        p->signal->real_timer.expires = jiffies + interval + 1;
-        add_timer(&p->signal->real_timer);
-}
 
 void it_real_fn(unsigned long __data)
 {
         struct task_struct * p = (struct task_struct *) __data;
+        unsigned long inc = p->signal->it_real_incr;
 
         send_group_sig_info(SIGALRM, SEND_SIG_PRIV, p);
 
@@ -141,14 +124,23 @@ void it_real_fn(unsigned long __data)
          * Now restart the timer if necessary.  We don't need any locking
          * here because do_setitimer makes sure we have finished running
          * before it touches anything.
+         * Note, we KNOW we are (or should be) at a jiffie edge here so
+         * we don't need the +1 stuff.  Also, we want to use the prior
+         * expire value so as to not "slip" a jiffie if we are late.
+         * Deal with requesting a time prior to "now" here rather than
+         * in add_timer.
          */
-        it_real_arm(p, p->signal->it_real_incr);
+        if (!inc)
+                return;
+        while (time_before_eq(p->signal->real_timer.expires, jiffies))
+                p->signal->real_timer.expires += inc;
+        add_timer(&p->signal->real_timer);
 }
 
 int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
 {
         struct task_struct *tsk = current;
-        unsigned long val, interval;
+        unsigned long val, interval, expires;
         cputime_t cval, cinterval, nval, ninterval;
 
         switch (which) {
@@ -164,7 +156,10 @@ again:
                 }
                 tsk->signal->it_real_incr =
                         timeval_to_jiffies(&value->it_interval);
-                it_real_arm(tsk, timeval_to_jiffies(&value->it_value));
+                expires = timeval_to_jiffies(&value->it_value);
+                if (expires)
+                        mod_timer(&tsk->signal->real_timer,
+                                  jiffies + 1 + expires);
                 spin_unlock_irq(&tsk->sighand->siglock);
                 if (ovalue) {
                         jiffies_to_timeval(val, &ovalue->it_value);