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Commit 1acdac10 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

futex: 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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Ulrich Drepper <drepper@redhat.com>
parent 3e1d7a62

include/linux/futex.h

+2 −1
Original line number Diff line number Diff line
@@ -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)

kernel/futex.c

+17 −7
Original line number Diff line number Diff line
@@ -1142,12 +1142,13 @@ 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, int 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);
@@ -1233,7 +1234,9 @@ static int futex_wait(u32 __user *uaddr, int fshared, 
			slack = current->timer_slack_ns;

			if (rt_task(current))

				slack = 0;

			hrtimer_init_on_stack(&t.timer, CLOCK_MONOTONIC,

			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);
@@ -1289,6 +1292,8 @@ static int futex_wait(u32 __user *uaddr, int fshared, 


		if (fshared)

			restart->futex.flags |= FLAGS_SHARED;

		if (clockrt)

			restart->futex.flags |= FLAGS_CLOCKRT;

		return -ERESTART_RESTARTBLOCK;

	}
@@ -1312,7 +1317,8 @@ static long futex_wait_restart(struct restart_block *restart) 
	if (restart->futex.flags & FLAGS_SHARED)

		fshared = 1;

	return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,

				restart->futex.bitset);

				restart->futex.bitset,

				restart->futex.flags & FLAGS_CLOCKRT);

}
@@ -1905,18 +1911,22 @@ void exit_robust_list(struct task_struct *curr) 
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;

	int fshared = 0;



	if (!(op & FUTEX_PRIVATE_FLAG))

		fshared = 1;



	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;