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Subjectfutex: make clock selectable for FUTEX_WAIT_BITSET
FUTEX_WAIT_BITSET could be used instead of FUTEX_WAIT by setting the
bit set to FUTEX_BITSET_MATCH_ANY, but FUTEX_WAIT uses CLOCK_REALTIME
while FUTEX_WAIT_BITSET uses CLOCK_MONOTONIC.

Add a flag to select CLOCK_REALTIME for FUTEX_WAIT_BITSET so glibc can
replace the FUTEX_WAIT logic which needs to do gettimeofday() calls
before and after the syscall to convert the absolute timeout to a
relative timeout for FUTEX_WAIT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/futex.h | 3 ++-
kernel/futex.c | 24 +++++++++++++++++-------
2 files changed, 19 insertions(+), 8 deletions(-)
Index: linux-2.6/include/linux/futex.h
===================================================================
--- linux-2.6.orig/include/linux/futex.h
+++ linux-2.6/include/linux/futex.h
@@ -25,7 +25,8 @@ union ktime;
#define FUTEX_WAKE_BITSET 10

#define FUTEX_PRIVATE_FLAG 128
-#define FUTEX_CMD_MASK ~FUTEX_PRIVATE_FLAG
+#define FUTEX_CLOCK_REALTIME 256
+#define FUTEX_CMD_MASK ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)

#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT | FUTEX_PRIVATE_FLAG)
#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE | FUTEX_PRIVATE_FLAG)
Index: linux-2.6/kernel/futex.c
===================================================================
--- linux-2.6.orig/kernel/futex.c
+++ linux-2.6/kernel/futex.c
@@ -1196,12 +1196,13 @@ handle_fault:
* In case we must use restart_block to restart a futex_wait,
* we encode in the 'flags' shared capability
*/
-#define FLAGS_SHARED 1
+#define FLAGS_SHARED 0x01
+#define FLAGS_CLOCKRT 0x02

static long futex_wait_restart(struct restart_block *restart);

static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
- u32 val, ktime_t *abs_time, u32 bitset)
+ u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
struct task_struct *curr = current;
DECLARE_WAITQUEUE(wait, curr);
@@ -1300,8 +1301,10 @@ static int futex_wait(u32 __user *uaddr,
slack = current->timer_slack_ns;
if (rt_task(current))
slack = 0;
- hrtimer_init_on_stack(&t.timer, CLOCK_MONOTONIC,
- HRTIMER_MODE_ABS);
+ hrtimer_init_on_stack(&t.timer,
+ clockrt ? CLOCK_REALTIME :
+ CLOCK_MONOTONIC,
+ HRTIMER_MODE_ABS);
hrtimer_init_sleeper(&t, current);
hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);

@@ -1356,6 +1359,8 @@ static int futex_wait(u32 __user *uaddr,

if (fshared)
restart->futex.flags |= FLAGS_SHARED;
+ if (clockrt)
+ restart->futex.flags |= FLAGS_CLOCKRT;
return -ERESTART_RESTARTBLOCK;
}

@@ -1379,7 +1384,8 @@ static long futex_wait_restart(struct re
if (restart->futex.flags & FLAGS_SHARED)
fshared = &current->mm->mmap_sem;
return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
- restart->futex.bitset);
+ restart->futex.bitset,
+ restart->futex.flags & FLAGS_CLOCKRT);
}


@@ -1993,18 +1999,22 @@ void exit_robust_list(struct task_struct
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
u32 __user *uaddr2, u32 val2, u32 val3)
{
- int ret = -ENOSYS;
+ int clockrt, ret = -ENOSYS;
int cmd = op & FUTEX_CMD_MASK;
struct rw_semaphore *fshared = NULL;

if (!(op & FUTEX_PRIVATE_FLAG))
fshared = &current->mm->mmap_sem;

+ clockrt = op & FUTEX_CLOCK_REALTIME;
+ if (clockrt && cmd != FUTEX_WAIT_BITSET)
+ return -ENOSYS;
+
switch (cmd) {
case FUTEX_WAIT:
val3 = FUTEX_BITSET_MATCH_ANY;
case FUTEX_WAIT_BITSET:
- ret = futex_wait(uaddr, fshared, val, timeout, val3);
+ ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
break;
case FUTEX_WAKE:
val3 = FUTEX_BITSET_MATCH_ANY;

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