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 <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Sripathi Kodi <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Dinakar Guniguntala <[email protected]>
Cc: Ulrich Drepper <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jakub Jelinek <[email protected]>
---
include/linux/futex.h | 4 +---
kernel/futex.c | 6 +-----
2 files changed, 2 insertions(+), 8 deletions(-)
diff --git a/include/linux/futex.h b/include/linux/futex.h
index b05519c..34956c8 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)
diff --git a/kernel/futex.c b/kernel/futex.c
index 3421e27..0c406a3 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2560,9 +2560,6 @@ 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);
@@ -2601,8 +2598,7 @@ 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);
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
Commit-ID: ba9c22f2c01cf5c88beed5a6b9e07d42e10bd358
Gitweb: http://git.kernel.org/tip/ba9c22f2c01cf5c88beed5a6b9e07d42e10bd358
Author: Darren Hart <[email protected]>
AuthorDate: Mon, 20 Apr 2009 22:22:22 -0700
Committer: Thomas Gleixner <[email protected]>
CommitDate: Thu, 30 Apr 2009 11:41:35 +0200
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 <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
---
include/linux/futex.h | 4 +---
kernel/futex.c | 6 +-----
2 files changed, 2 insertions(+), 8 deletions(-)
diff --git a/include/linux/futex.h b/include/linux/futex.h
index b05519c..34956c8 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)
diff --git a/kernel/futex.c b/kernel/futex.c
index 6d2daa4..aec8bf8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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);