futex: remove FUTEX_REQUEUE_PI (non CMP)

The new requeue PI futex op codes were modeled after the existing
FUTEX_REQUEUE and FUTEX_CMP_REQUEUE calls. I was unaware at the time
that FUTEX_REQUEUE was only around for compatibility reasons and
shouldn't be used in new code. Ulrich Drepper elaborates on this in his
Futexes are Tricky paper: http://people.redhat.com/drepper/futex.pdf.
The deprecated call doesn't catch changes to the futex corresponding to
the destination futex which can lead to deadlock.

Therefor, I feel it best to remove FUTEX_REQUEUE_PI and leave only
FUTEX_CMP_REQUEUE_PI as there are not yet any existing users of the API.
This patch does change the OP code value of FUTEX_CMP_REQUEUE_PI to 12
from 13. Since my test case is the only known user of this API, I felt
this was the right thing to do, rather than leave a hole in the
enumeration.

I chose to continue using the _CMP_ modifier in the OP code to make it
explicit to the user that the test is being done.

Builds, boots, and ran several hundred iterations requeue_pi.c.

Signed-off-by: Darren Hart <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/futex.h

···
 #define FUTEX_WAIT_BITSET	9
 #define FUTEX_WAKE_BITSET	10
 #define FUTEX_WAIT_REQUEUE_PI	11
-#define FUTEX_REQUEUE_PI	12
-#define FUTEX_CMP_REQUEUE_PI	13
+#define FUTEX_CMP_REQUEUE_PI	12
 
 #define FUTEX_PRIVATE_FLAG	128
 #define FUTEX_CLOCK_REALTIME	256
···
 #define FUTEX_WAKE_BITSET_PRIVATE	(FUTEX_WAKE_BITS | FUTEX_PRIVATE_FLAG)
 #define FUTEX_WAIT_REQUEUE_PI_PRIVATE	(FUTEX_WAIT_REQUEUE_PI | \
 					 FUTEX_PRIVATE_FLAG)
-#define FUTEX_REQUEUE_PI_PRIVATE	(FUTEX_REQUEUE_PI | FUTEX_PRIVATE_FLAG)
 #define FUTEX_CMP_REQUEUE_PI_PRIVATE	(FUTEX_CMP_REQUEUE_PI | \
 					 FUTEX_PRIVATE_FLAG)
 

kernel/futex.c

···
 		ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
 					    clockrt, uaddr2);
 		break;
-	case FUTEX_REQUEUE_PI:
-		ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 1);
-		break;
 	case FUTEX_CMP_REQUEUE_PI:
 		ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
 				    1);
···
 	 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
 	 */
 	if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
-	    cmd == FUTEX_REQUEUE_PI || cmd == FUTEX_CMP_REQUEUE_PI ||
-	    cmd == FUTEX_WAKE_OP)
+	    cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
 		val2 = (u32) (unsigned long) utime;
 
 	return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);