linux-kernel - [PATCH 5.5 151/176] lib/vdso: Update coarse timekeeper unconditionally

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Date:   Tue,  3 Mar 2020 18:43:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 5.5 151/176] lib/vdso: Update coarse timekeeper unconditionally

From: Thomas Gleixner <tglx@...utronix.de>

commit 9f24c540f7f8eb3a981528da9a9a636a5bdf5987 upstream.

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 skip
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@...utronix.de>
Link: https://lore.kernel.org/r/20200114185946.765577901@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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);