mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-21 09:05:20 -04:00
Code Issues Packages Projects Releases Wiki Activity

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

Browse Source 
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
This commit is contained in:
Thomas Weißschuh
2026-02-27 07:43:21 +01:00
committed by Thomas Gleixner
parent 08cd5e1de8
commit ed78b7b2c5
2 changed files with 31 additions and 42 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
include/vdso/helpers.h
View File

@@ -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)
{

51
lib/vdso/gettimeofday.c
View File

@@ -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)