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, 9 insertions, 10 deletions

diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 50f24eea6cd0..dff27c471ea6 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -141,24 +141,23 @@ asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
                 struct compat_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;
         int val2 = 0;
 
         if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
-                if (get_compat_timespec(&t, utime))
+                if (get_compat_timespec(&ts, utime))
                         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;
         }
         if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
                 val2 = (int) (unsigned long) utime;
 
-        return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
+        return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 }