include/vdso/helpers.h | 22 +++++++++++++++++- lib/vdso/gettimeofday.c | 51 +++++++--------------------------------- 2 files changed, 31 insertions(+), 42 deletions(-)
The following commit has been merged into the timers/vdso branch of tip:
Commit-ID: ed78b7b2c5ae679960469c0f679539c427e051ab
Gitweb: https://git.kernel.org/tip/ed78b7b2c5ae679960469c0f679539c427e051ab
Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
AuthorDate: Fri, 27 Feb 2026 07:43:21 +01:00
Committer: Thomas Gleixner <tglx@kernel.org>
CommitterDate: Wed, 11 Mar 2026 10:27:35 +01:00
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: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260227-vdso-cleanups-v1-2-c848b4bc4850@linutronix.de
---
include/vdso/helpers.h | 22 +++++++++++++++++-
lib/vdso/gettimeofday.c | 51 +++++++---------------------------------
2 files changed, 31 insertions(+), 42 deletions(-)
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
index 1a5ee9d..9ccf6b5 100644
--- a/include/vdso/helpers.h
+++ b/include/vdso/helpers.h
@@ -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)
{
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 4939ee8..e493696 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -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)
- return do_hres_timens(vd, vc, clk, ts);
- cpu_relax();
- }
- smp_rmb();
+ if (vdso_read_begin_timens(vc, &seq))
+ return do_hres_timens(vd, vc, clk, ts);
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)
- return do_coarse_timens(vd, vc, clk, ts);
- cpu_relax();
- }
- smp_rmb();
+ if (vdso_read_begin_timens(vc, &seq))
+ return do_coarse_timens(vd, vc, clk, ts);
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) {
- 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();
+ 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;
}
- smp_rmb();
/* Auxclock disabled? */
if (vc->clock_mode == VDSO_CLOCKMODE_NONE)© 2016 - 2026 Red Hat, Inc.