Commit ed78b7b2 authored by Thomas Weißschuh's avatar Thomas Weißschuh Committed by Thomas Gleixner
Browse files

vdso/gettimeofday: Add a helper to read the sequence lock of a time namespace aware clock 



Currently there are three different open-coded variants of a time
namespace aware variant of vdso_read_begin(). They make the code hard to
read and introduce an inconsistency, as only the first copy uses
unlikely().

Split the code into a shared helper function.
Move that next to the definition of the regular vdso_read_begin(), so
that any future changes can be kept in sync easily.

Signed-off-by: default avatarThomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260227-vdso-cleanups-v1-2-c848b4bc4850@linutronix.de
parent 08cd5e1d

include/vdso/helpers.h

+22 −0
Original line number Diff line number Diff line
@@ -18,6 +18,28 @@ static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc) 
	return seq;

}



/*

 * Variant of vdso_read_begin() to handle VDSO_CLOCKMODE_TIMENS.

 *

 * Time namespace enabled tasks have a special VVAR page installed which has

 * vc->seq set to 1 and vc->clock_mode set to VDSO_CLOCKMODE_TIMENS. For non

 * time namespace affected tasks this does not affect performance because if

 * vc->seq is odd, i.e. a concurrent update is in progress the extra check for

 * vc->clock_mode is just a few extra instructions while spin waiting for

 * vc->seq to become even again.

 */

static __always_inline bool vdso_read_begin_timens(const struct vdso_clock *vc, u32 *seq)

{

	while (unlikely((*seq = READ_ONCE(vc->seq)) & 1)) {

		if (IS_ENABLED(CONFIG_TIME_NS) && vc->clock_mode == VDSO_CLOCKMODE_TIMENS)

			return true;

		cpu_relax();

	}

	smp_rmb();



	return false;

}



static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,

					   u32 start)

{

lib/vdso/gettimeofday.c

+9 −42
Original line number Diff line number Diff line
@@ -158,24 +158,8 @@ bool do_hres(const struct vdso_time_data *vd, const struct vdso_clock *vc, 
		return false;



	do {

		/*

		 * Open coded function vdso_read_begin() to handle

		 * VDSO_CLOCKMODE_TIMENS. Time namespace enabled tasks have a

		 * special VVAR page installed which has vc->seq set to 1 and

		 * vc->clock_mode set to VDSO_CLOCKMODE_TIMENS. For non time

		 * namespace affected tasks this does not affect performance

		 * because if vc->seq is odd, i.e. a concurrent update is in

		 * progress the extra check for vc->clock_mode is just a few

		 * extra instructions while spin waiting for vc->seq to become

		 * even again.

		 */

		while (unlikely((seq = READ_ONCE(vc->seq)) & 1)) {

			if (IS_ENABLED(CONFIG_TIME_NS) &&

			    vc->clock_mode == VDSO_CLOCKMODE_TIMENS)

		if (vdso_read_begin_timens(vc, &seq))

			return do_hres_timens(vd, vc, clk, ts);

			cpu_relax();

		}

		smp_rmb();



		if (!vdso_get_timestamp(vd, vc, clk, &sec, &ns))

			return false;
@@ -223,17 +207,8 @@ bool do_coarse(const struct vdso_time_data *vd, const struct vdso_clock *vc, 
	u32 seq;



	do {

		/*

		 * Open coded function vdso_read_begin() to handle

		 * VDSO_CLOCK_TIMENS. See comment in do_hres().

		 */

		while ((seq = READ_ONCE(vc->seq)) & 1) {

			if (IS_ENABLED(CONFIG_TIME_NS) &&

			    vc->clock_mode == VDSO_CLOCKMODE_TIMENS)

		if (vdso_read_begin_timens(vc, &seq))

			return do_coarse_timens(vd, vc, clk, ts);

			cpu_relax();

		}

		smp_rmb();



		ts->tv_sec = vdso_ts->sec;

		ts->tv_nsec = vdso_ts->nsec;
@@ -256,20 +231,12 @@ bool do_aux(const struct vdso_time_data *vd, clockid_t clock, struct __kernel_ti 
	vc = &vd->aux_clock_data[idx];



	do {

		/*

		 * Open coded function vdso_read_begin() to handle

		 * VDSO_CLOCK_TIMENS. See comment in do_hres().

		 */

		while ((seq = READ_ONCE(vc->seq)) & 1) {

			if (IS_ENABLED(CONFIG_TIME_NS) && vc->clock_mode == VDSO_CLOCKMODE_TIMENS) {

		if (vdso_read_begin_timens(vc, &seq)) {

			vd = __arch_get_vdso_u_timens_data(vd);

			vc = &vd->aux_clock_data[idx];

			/* Re-read from the real time data page */

			continue;

		}

			cpu_relax();

		}

		smp_rmb();



		/* Auxclock disabled? */

		if (vc->clock_mode == VDSO_CLOCKMODE_NONE)