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 <dvhltc@us.ibm.com>
LKML-Reference: <49ED580E.1050502@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 1 insertions, 3 deletions

diff --git a/include/linux/futex.h b/include/linux/futex.h
index b05519ca9e57..34956c8fdebf 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -24,8 +24,7 @@ union ktime;
 #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
@@ -43,7 +42,6 @@ union ktime;
 #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)