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Subject[patch 02/15] lib/vdso: Update coarse timekeeper unconditionally
The low resolution parts of the VDSO, i.e.:

clock_gettime(CLOCK_*_COARSE)
clock_getres()
time()

can be used even if there is no VDSO capable clocksource. But if an
architecture opts out of the VDSO data update then this information
becomes stale. This affects ARM when there is no architected timer
available. The lack of update causes userspace to use stale data
forever.

Make the update of the low resolution parts unconditional and only
prevent the update of the high resolution parts if the architecture
requests it.

Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/vsyscall.c | 37 +++++++++++++++++--------------------
1 file changed, 17 insertions(+), 20 deletions(-)

--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -28,11 +28,6 @@ static inline void update_vdso_data(stru
vdata[CS_RAW].mult = tk->tkr_raw.mult;
vdata[CS_RAW].shift = tk->tkr_raw.shift;

- /* CLOCK_REALTIME */
- vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME];
- vdso_ts->sec = tk->xtime_sec;
- vdso_ts->nsec = tk->tkr_mono.xtime_nsec;
-
/* CLOCK_MONOTONIC */
vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_MONOTONIC];
vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
@@ -70,12 +65,6 @@ static inline void update_vdso_data(stru
vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_TAI];
vdso_ts->sec = tk->xtime_sec + (s64)tk->tai_offset;
vdso_ts->nsec = tk->tkr_mono.xtime_nsec;
-
- /*
- * Read without the seqlock held by clock_getres().
- * Note: No need to have a second copy.
- */
- WRITE_ONCE(vdata[CS_HRES_COARSE].hrtimer_res, hrtimer_resolution);
}

void update_vsyscall(struct timekeeper *tk)
@@ -84,20 +73,17 @@ void update_vsyscall(struct timekeeper *
struct vdso_timestamp *vdso_ts;
u64 nsec;

- if (!__arch_update_vdso_data()) {
- /*
- * Some architectures might want to skip the update of the
- * data page.
- */
- return;
- }
-
/* copy vsyscall data */
vdso_write_begin(vdata);

vdata[CS_HRES_COARSE].clock_mode = __arch_get_clock_mode(tk);
vdata[CS_RAW].clock_mode = __arch_get_clock_mode(tk);

+ /* CLOCK_REALTIME also required for time() */
+ vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME];
+ vdso_ts->sec = tk->xtime_sec;
+ vdso_ts->nsec = tk->tkr_mono.xtime_nsec;
+
/* CLOCK_REALTIME_COARSE */
vdso_ts = &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME_COARSE];
vdso_ts->sec = tk->xtime_sec;
@@ -110,7 +96,18 @@ void update_vsyscall(struct timekeeper *
nsec = nsec + tk->wall_to_monotonic.tv_nsec;
vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);

- update_vdso_data(vdata, tk);
+ /*
+ * Read without the seqlock held by clock_getres().
+ * Note: No need to have a second copy.
+ */
+ WRITE_ONCE(vdata[CS_HRES_COARSE].hrtimer_res, hrtimer_resolution);
+
+ /*
+ * Architectures can opt out of updating the high resolution part
+ * of the VDSO.
+ */
+ if (__arch_update_vdso_data())
+ update_vdso_data(vdata, tk);

__arch_update_vsyscall(vdata, tk);

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