Merge tag 'timers-urgent-2020-01-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fixes from Thomas Gleixner:
 "Two fixes for the generic VDSO code which missed 5.5:

   - Make the update to the coarse timekeeper unconditional.

     This is required because the coarse timekeeper interfaces in the
     VDSO do not depend on a VDSO capable clocksource. If the system
     does not have a VDSO capable clocksource and the update is
     depending on the VDSO capable clocksource, the coarse VDSO
     interfaces would operate on stale data forever.

   - Invert the logic of __arch_update_vdso_data() to avoid further head
     scratching.

     Tripped over this several times while analyzing the update problem
     above"

* tag 'timers-urgent-2020-01-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  lib/vdso: Update coarse timekeeper unconditionally
  lib/vdso: Make __arch_update_vdso_data() logic understandable

Author: torvalds

arch/arm/include/asm/vdso/vsyscall.h

@@ -34,9 +34,9 @@ struct vdso_data *__arm_get_k_vdso_data(void)
 #define __arch_get_k_vdso_data __arm_get_k_vdso_data
 
 static __always_inline
-int __arm_update_vdso_data(void)
+bool __arm_update_vdso_data(void)
 {
-	return !cntvct_ok;
+	return cntvct_ok;
 }
 #define __arch_update_vdso_data __arm_update_vdso_data
 

include/asm-generic/vdso/vsyscall.h

@@ -12,9 +12,9 @@ static __always_inline struct vdso_data *__arch_get_k_vdso_data(void)
 #endif /* __arch_get_k_vdso_data */
 
 #ifndef __arch_update_vdso_data
-static __always_inline int __arch_update_vdso_data(void)
+static __always_inline bool __arch_update_vdso_data(void)
 {
-	return 0;
+	return true;
 }
 #endif /* __arch_update_vdso_data */
 

kernel/time/vsyscall.c

@@ -28,11 +28,6 @@ static inline void update_vdso_data(struct vdso_data *vdata,
 	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(struct vdso_data *vdata,
 	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 *tk)
 	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 *tk)
 	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);