Messages in this thread Patch in this message | | | Date | Mon, 20 Apr 2009 22:22:22 -0700 | From | Darren Hart <> | Subject | [PATCH][tip:core/futexes][next][rt] 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> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sripathi Kodi <sripathik@in.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: John Stultz <johnstul@us.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Dinakar Guniguntala <dino@in.ibm.com> Cc: Ulrich Drepper <drepper@redhat.com> Cc: Eric Dumazet <dada1@cosmosbay.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Jakub Jelinek <jakub@redhat.com> ---
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
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