Make futex_wait() use an hrtimer for timeout

This patch modifies futex_wait() to use an hrtimer + schedule() in place of
schedule_timeout().

schedule_timeout() is tick based, therefore the timeout granularity is the
tick (1 ms, 4 ms or 10 ms depending on HZ).  By using a high resolution timer
for timeout wakeup, we can attain a much finer timeout granularity (in the
microsecond range).  This parallels what is already done for futex_lock_pi().

The timeout passed to the syscall is no longer converted to jiffies and is
therefore passed to do_futex() and futex_wait() as an absolute ktime_t
therefore keeping nanosecond resolution.

Also this removes the need to pass the nanoseconds timeout part to
futex_lock_pi() in val2.

In futex_wait(), if there is no timeout then a regular schedule() is
performed.  Otherwise, an hrtimer is fired before schedule() is called.

[akpm@linux-foundation.org: fix `make headers_check']
Signed-off-by: Sebastien Dugue <sebastien.dugue@bull.net>
Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 45 insertions, 44 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 685ee2362a5..e1246ccbf89 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1001,16 +1001,16 @@ static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
 }
 
 static long futex_wait_restart(struct restart_block *restart);
-static int futex_wait_abstime(u32 __user *uaddr, u32 val,
-                        int timed, unsigned long abs_time)
+static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 {
         struct task_struct *curr = current;
         DECLARE_WAITQUEUE(wait, curr);
         struct futex_hash_bucket *hb;
         struct futex_q q;
-        unsigned long time_left = 0;
         u32 uval;
         int ret;
+        struct hrtimer_sleeper t;
+        int rem = 0;
 
         q.pi_state = NULL;
  retry:
@@ -1088,20 +1088,29 @@ static int futex_wait_abstime(u32 __user *uaddr, u32 val,
          * !plist_node_empty() is safe here without any lock.
          * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
          */
-        time_left = 0;
         if (likely(!plist_node_empty(&q.list))) {
-                unsigned long rel_time;
-
-                if (timed) {
-                        unsigned long now = jiffies;
-                        if (time_after(now, abs_time))
-                                rel_time = 0;
-                        else
-                                rel_time = abs_time - now;
-                } else
-                        rel_time = MAX_SCHEDULE_TIMEOUT;
+                if (!abs_time)
+                        schedule();
+                else {
+                        hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+                        hrtimer_init_sleeper(&t, current);
+                        t.timer.expires = *abs_time;
+
+                        hrtimer_start(&t.timer, t.timer.expires, HRTIMER_MODE_ABS);
+
+                        /*
+                         * the timer could have already expired, in which
+                         * case current would be flagged for rescheduling.
+                         * Don't bother calling schedule.
+                         */
+                        if (likely(t.task))
+                                schedule();
+
+                        hrtimer_cancel(&t.timer);
 
-                time_left = schedule_timeout(rel_time);
+                        /* Flag if a timeout occured */
+                        rem = (t.task == NULL);
+                }
         }
         __set_current_state(TASK_RUNNING);
 
@@ -1113,14 +1122,14 @@ static int futex_wait_abstime(u32 __user *uaddr, u32 val,
         /* If we were woken (and unqueued), we succeeded, whatever. */
         if (!unqueue_me(&q))
                 return 0;
-        if (time_left == 0)
+        if (rem)
                 return -ETIMEDOUT;
 
         /*
          * We expect signal_pending(current), but another thread may
          * have handled it for us already.
          */
-        if (time_left == MAX_SCHEDULE_TIMEOUT)
+        if (!abs_time)
                 return -ERESTARTSYS;
         else {
                 struct restart_block *restart;
@@ -1128,8 +1137,7 @@ static int futex_wait_abstime(u32 __user *uaddr, u32 val,
                 restart->fn = futex_wait_restart;
                 restart->arg0 = (unsigned long)uaddr;
                 restart->arg1 = (unsigned long)val;
-                restart->arg2 = (unsigned long)timed;
-                restart->arg3 = abs_time;
+                restart->arg2 = (unsigned long)abs_time;
                 return -ERESTART_RESTARTBLOCK;
         }
 
@@ -1141,21 +1149,15 @@ static int futex_wait_abstime(u32 __user *uaddr, u32 val,
         return ret;
 }
 
-static int futex_wait(u32 __user *uaddr, u32 val, unsigned long rel_time)
-{
-        int timed = (rel_time != MAX_SCHEDULE_TIMEOUT);
-        return futex_wait_abstime(uaddr, val, timed, jiffies+rel_time);
-}
 
 static long futex_wait_restart(struct restart_block *restart)
 {
         u32 __user *uaddr = (u32 __user *)restart->arg0;
         u32 val = (u32)restart->arg1;
-        int timed = (int)restart->arg2;
-        unsigned long abs_time = restart->arg3;
+        ktime_t *abs_time = (ktime_t *)restart->arg2;
 
         restart->fn = do_no_restart_syscall;
-        return (long)futex_wait_abstime(uaddr, val, timed, abs_time);
+        return (long)futex_wait(uaddr, val, abs_time);
 }
 
 
@@ -1165,8 +1167,8 @@ static long futex_wait_restart(struct restart_block *restart)
  * if there are waiters then it will block, it does PI, etc. (Due to
  * races the kernel might see a 0 value of the futex too.)
  */
-static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
-                         long nsec, int trylock)
+static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
+                         int trylock)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct task_struct *curr = current;
@@ -1178,11 +1180,11 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
         if (refill_pi_state_cache())
                 return -ENOMEM;
 
-        if (sec != MAX_SCHEDULE_TIMEOUT) {
+        if (time) {
                 to = &timeout;
                 hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
-                to->timer.expires = ktime_set(sec, nsec);
+                to->timer.expires = *time;
         }
 
         q.pi_state = NULL;
@@ -1818,7 +1820,7 @@ void exit_robust_list(struct task_struct *curr)
         }
 }
 
-long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 u32 __user *uaddr2, u32 val2, u32 val3)
 {
         int ret;
@@ -1844,13 +1846,13 @@ long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
                 ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
                 break;
         case FUTEX_LOCK_PI:
-                ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
+                ret = futex_lock_pi(uaddr, val, timeout, 0);
                 break;
         case FUTEX_UNLOCK_PI:
                 ret = futex_unlock_pi(uaddr);
                 break;
         case FUTEX_TRYLOCK_PI:
-                ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
+                ret = futex_lock_pi(uaddr, 0, timeout, 1);
                 break;
         default:
                 ret = -ENOSYS;
@@ -1863,21 +1865,20 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
                           struct timespec __user *utime, u32 __user *uaddr2,
                           u32 val3)
 {
-        struct timespec t;
-        unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
+        struct timespec ts;
+        ktime_t t, *tp = NULL;
         u32 val2 = 0;
 
         if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
-                if (copy_from_user(&t, utime, sizeof(t)) != 0)
+                if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
                         return -EFAULT;
-                if (!timespec_valid(&t))
+                if (!timespec_valid(&ts))
                         return -EINVAL;
+
+                t = timespec_to_ktime(ts);
                 if (op == FUTEX_WAIT)
-                        timeout = timespec_to_jiffies(&t) + 1;
-                else {
-                        timeout = t.tv_sec;
-                        val2 = t.tv_nsec;
-                }
+                        t = ktime_add(ktime_get(), t);
+                tp = &t;
         }
         /*
          * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
@@ -1885,7 +1886,7 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
         if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
                 val2 = (u32) (unsigned long) utime;
 
-        return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
+        return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 }
 
 static int futexfs_get_sb(struct file_system_type *fs_type,