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Commit ba9c22f2 authored by Darren Hart's avatar Darren Hart Committed by Thomas Gleixner
Browse files

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: default avatarDarren Hart <dvhltc@us.ibm.com>
LKML-Reference: <49ED580E.1050502@us.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent a5a2a0c7

include/linux/futex.h

+1 −3
Original line number Diff line number Diff line
@@ -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)

kernel/futex.c

+1 −5
Original line number Diff line number Diff line
@@ -2555,9 +2555,6 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, 
		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);
@@ -2596,8 +2593,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, 
	 * 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);