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futex: remove FUTEX_REQUEUE_PI (non CMP)

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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>
This commit is contained in:
Darren Hart 2009-04-20 22:22:22 -07:00 • committed by Thomas Gleixner
parent a5a2a0c7fa
commit ba9c22f2c0
2 changed files with 2 additions and 8 deletions
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4
include/linux/futex.h
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@ -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)