futex: add FUTEX_HAS_TIMEOUT flag to restart.futex.flags
Darren Hart [Fri, 3 Apr 2009 20:40:22 +0000 (13:40 -0700)]
Currently restart is only used if there is a timeout. The requeue_pi
functionality requires restarting to futex_lock_pi() on signal after
wakeup in futex_wait_requeue_pi() regardless of if there was a timeout
or not. Using 0 for the timeout value is confusing as that could
indicate an expired timer. The flag makes this explicit. While the
check is not technically needed in futex_wait_restart(), doing so
makes the code consistent with and will avoid confusion should the
need arise to restart wait without a timeout.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/futex.c

index af831fb..6b597cf 100644 (file)
@@ -1252,6 +1252,7 @@ handle_fault:
  */
 #define FLAGS_SHARED           0x01
 #define FLAGS_CLOCKRT          0x02
+#define FLAGS_HAS_TIMEOUT      0x04
 
 static long futex_wait_restart(struct restart_block *restart);
 
@@ -1486,7 +1487,7 @@ retry_private:
        restart->futex.val = val;
        restart->futex.time = abs_time->tv64;
        restart->futex.bitset = bitset;
-       restart->futex.flags = 0;
+       restart->futex.flags = FLAGS_HAS_TIMEOUT;
 
        if (fshared)
                restart->futex.flags |= FLAGS_SHARED;
@@ -1510,13 +1511,16 @@ static long futex_wait_restart(struct restart_block *restart)
 {
        u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
        int fshared = 0;
-       ktime_t t;
+       ktime_t t, *tp = NULL;
 
-       t.tv64 = restart->futex.time;
+       if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+               t.tv64 = restart->futex.time;
+               tp = &t;
+       }
        restart->fn = do_no_restart_syscall;
        if (restart->futex.flags & FLAGS_SHARED)
                fshared = 1;
-       return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
+       return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
                                restart->futex.bitset,
                                restart->futex.flags & FLAGS_CLOCKRT);
 }