From ed78b7b2c5ae679960469c0f679539c427e051ab Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= Date: Fri, 27 Feb 2026 07:43:21 +0100 Subject: [PATCH] vdso/gettimeofday: Add a helper to read the sequence lock of a time namespace aware clock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Thomas Gleixner 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 1a5ee9d9052c..9ccf6b53ef50 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 4939ee86af65..e49369676928 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)