futex: make clock selectable for FUTEX_WAIT_BITSET

FUTEX_WAIT_BITSET could be used instead of FUTEX_WAIT by setting the
bit set to FUTEX_BITSET_MATCH_ANY, but FUTEX_WAIT uses CLOCK_REALTIME
while FUTEX_WAIT_BITSET uses CLOCK_MONOTONIC.

Add a flag to select CLOCK_REALTIME for FUTEX_WAIT_BITSET so glibc can
replace the FUTEX_WAIT logic which needs to do gettimeofday() calls
before and after the syscall to convert the absolute timeout to a
relative timeout for FUTEX_WAIT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ulrich Drepper <drepper@redhat.com>

2 files changed, 19 insertions, 8 deletions

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 8f627b9ae2b1..3bf5bb5a34f9 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -25,7 +25,8 @@ union ktime;
 #define FUTEX_WAKE_BITSET       10
 
 #define FUTEX_PRIVATE_FLAG      128
-#define FUTEX_CMD_MASK          ~FUTEX_PRIVATE_FLAG
+#define FUTEX_CLOCK_REALTIME    256
+#define FUTEX_CMD_MASK          ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
 
 #define FUTEX_WAIT_PRIVATE      (FUTEX_WAIT | FUTEX_PRIVATE_FLAG)
 #define FUTEX_WAKE_PRIVATE      (FUTEX_WAKE | FUTEX_PRIVATE_FLAG)
diff --git a/kernel/futex.c b/kernel/futex.c
index e10c5c8786a6..ba0d3b83c091 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1142,12 +1142,13 @@ handle_fault:
  * In case we must use restart_block to restart a futex_wait,
  * we encode in the 'flags' shared capability
  */
-#define FLAGS_SHARED  1
+#define FLAGS_SHARED            0x01
+#define FLAGS_CLOCKRT           0x02
 
 static long futex_wait_restart(struct restart_block *restart);
 
 static int futex_wait(u32 __user *uaddr, int fshared,
-                      u32 val, ktime_t *abs_time, u32 bitset)
+                      u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
 {
         struct task_struct *curr = current;
         DECLARE_WAITQUEUE(wait, curr);
@@ -1233,8 +1234,10 @@ static int futex_wait(u32 __user *uaddr, int fshared,
                         slack = current->timer_slack_ns;
                         if (rt_task(current))
                                 slack = 0;
-                        hrtimer_init_on_stack(&t.timer, CLOCK_MONOTONIC,
-                                                HRTIMER_MODE_ABS);
+                        hrtimer_init_on_stack(&t.timer,
+                                              clockrt ? CLOCK_REALTIME :
+                                              CLOCK_MONOTONIC,
+                                              HRTIMER_MODE_ABS);
                         hrtimer_init_sleeper(&t, current);
                         hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);
 
@@ -1289,6 +1292,8 @@ static int futex_wait(u32 __user *uaddr, int fshared,
 
                 if (fshared)
                         restart->futex.flags |= FLAGS_SHARED;
+                if (clockrt)
+                        restart->futex.flags |= FLAGS_CLOCKRT;
                 return -ERESTART_RESTARTBLOCK;
         }
 
@@ -1312,7 +1317,8 @@ static long futex_wait_restart(struct restart_block *restart)
         if (restart->futex.flags & FLAGS_SHARED)
                 fshared = 1;
         return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
-                                restart->futex.bitset);
+                                restart->futex.bitset,
+                                restart->futex.flags & FLAGS_CLOCKRT);
 }
 
 
@@ -1905,18 +1911,22 @@ void exit_robust_list(struct task_struct *curr)
 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 u32 __user *uaddr2, u32 val2, u32 val3)
 {
-        int ret = -ENOSYS;
+        int clockrt, ret = -ENOSYS;
         int cmd = op & FUTEX_CMD_MASK;
         int fshared = 0;
 
         if (!(op & FUTEX_PRIVATE_FLAG))
                 fshared = 1;
 
+        clockrt = op & FUTEX_CLOCK_REALTIME;
+        if (clockrt && cmd != FUTEX_WAIT_BITSET)
+                return -ENOSYS;
+
         switch (cmd) {
         case FUTEX_WAIT:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAIT_BITSET:
-                ret = futex_wait(uaddr, fshared, val, timeout, val3);
+                ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
                 break;
         case FUTEX_WAKE:
                 val3 = FUTEX_BITSET_MATCH_ANY;