hrtimer: Handle remaining time proper for TIME_LOW_RES

commit 203cbf77de59fc8f13502dcfd11350c6d4a5c95f upstream.

If CONFIG_TIME_LOW_RES is enabled we add a jiffie to the relative timeout to
prevent short sleeps, but we do not account for that in interfaces which
retrieve the remaining time.

Helge observed that timerfd can return a remaining time larger than the
relative timeout. That's not expected and breaks userland test programs.

Store the information that the timer was armed relative and provide functions
to adjust the remaining time. To avoid bloating the hrtimer struct make state
a u8, which as a bonus results in better code on x86 at least.

Reported-and-tested-by: Helge Deller <deller@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: dhowells@redhat.com
Link: http://lkml.kernel.org/r/20160114164159.273328486@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 76dd4f0da5ca9907572bea19f4b0d0dbe8ad06eb..2ead22dd74a00896d24fdb937242e8ba36a77cfe 100644 (file)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -87,7 +87,8 @@ enum hrtimer_restart {
  * @function:  timer expiry callback function
  * @base:      pointer to the timer base (per cpu and per clock)
  * @state:     state information (See bit values above)
- * @start_pid: timer statistics field to store the pid of the task which
+ * @is_rel:    Set if the timer was armed relative
+ * @start_pid:  timer statistics field to store the pid of the task which
  *             started the timer
  * @start_site:        timer statistics field to store the site where the timer
  *             was started
@@ -101,7 +102,8 @@ struct hrtimer {
        ktime_t                         _softexpires;
        enum hrtimer_restart            (*function)(struct hrtimer *);
        struct hrtimer_clock_base       *base;
-       unsigned long                   state;
+       u8                              state;
+       u8                              is_rel;
 #ifdef CONFIG_TIMER_STATS
        int                             start_pid;
        void                            *start_site;
@@ -321,6 +323,27 @@ static inline void clock_was_set_delayed(void) { }
 
 #endif
 
+static inline ktime_t
+__hrtimer_expires_remaining_adjusted(const struct hrtimer *timer, ktime_t now)
+{
+       ktime_t rem = ktime_sub(timer->node.expires, now);
+
+       /*
+        * Adjust relative timers for the extra we added in
+        * hrtimer_start_range_ns() to prevent short timeouts.
+        */
+       if (IS_ENABLED(CONFIG_TIME_LOW_RES) && timer->is_rel)
+               rem.tv64 -= hrtimer_resolution;
+       return rem;
+}
+
+static inline ktime_t
+hrtimer_expires_remaining_adjusted(const struct hrtimer *timer)
+{
+       return __hrtimer_expires_remaining_adjusted(timer,
+                                                   timer->base->get_time());
+}
+
 extern void clock_was_set(void);
 #ifdef CONFIG_TIMERFD
 extern void timerfd_clock_was_set(void);
@@ -390,7 +413,12 @@ static inline void hrtimer_restart(struct hrtimer *timer)
 }
 
 /* Query timers: */
-extern ktime_t hrtimer_get_remaining(const struct hrtimer *timer);
+extern ktime_t __hrtimer_get_remaining(const struct hrtimer *timer, bool adjust);
+
+static inline ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
+{
+       return __hrtimer_get_remaining(timer, false);
+}
 
 extern u64 hrtimer_get_next_event(void);
 

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 435b8850dd80a300c11ad128bc0cf51e3c23e15a..fa909f9fd5591801968523032e00f8fe816fb23f 100644 (file)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -897,10 +897,10 @@ static int enqueue_hrtimer(struct hrtimer *timer,
  */
 static void __remove_hrtimer(struct hrtimer *timer,
                             struct hrtimer_clock_base *base,
-                            unsigned long newstate, int reprogram)
+                            u8 newstate, int reprogram)
 {
        struct hrtimer_cpu_base *cpu_base = base->cpu_base;
-       unsigned int state = timer->state;
+       u8 state = timer->state;
 
        timer->state = newstate;
        if (!(state & HRTIMER_STATE_ENQUEUED))
@@ -930,7 +930,7 @@ static inline int
 remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base, bool restart)
 {
        if (hrtimer_is_queued(timer)) {
-               unsigned long state = timer->state;
+               u8 state = timer->state;
                int reprogram;
 
                /*
@@ -954,6 +954,22 @@ remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base, bool rest
        return 0;
 }
 
+static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
+                                           const enum hrtimer_mode mode)
+{
+#ifdef CONFIG_TIME_LOW_RES
+       /*
+        * CONFIG_TIME_LOW_RES indicates that the system has no way to return
+        * granular time values. For relative timers we add hrtimer_resolution
+        * (i.e. one jiffie) to prevent short timeouts.
+        */
+       timer->is_rel = mode & HRTIMER_MODE_REL;
+       if (timer->is_rel)
+               tim = ktime_add_safe(tim, ktime_set(0, hrtimer_resolution));
+#endif
+       return tim;
+}
+
 /**
  * hrtimer_start_range_ns - (re)start an hrtimer on the current CPU
  * @timer:     the timer to be added
@@ -974,19 +990,10 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
        /* Remove an active timer from the queue: */
        remove_hrtimer(timer, base, true);
 
-       if (mode & HRTIMER_MODE_REL) {
+       if (mode & HRTIMER_MODE_REL)
                tim = ktime_add_safe(tim, base->get_time());
-               /*
-                * CONFIG_TIME_LOW_RES is a temporary way for architectures
-                * to signal that they simply return xtime in
-                * do_gettimeoffset(). In this case we want to round up by
-                * resolution when starting a relative timer, to avoid short
-                * timeouts. This will go away with the GTOD framework.
-                */
-#ifdef CONFIG_TIME_LOW_RES
-               tim = ktime_add_safe(tim, ktime_set(0, hrtimer_resolution));
-#endif
-       }
+
+       tim = hrtimer_update_lowres(timer, tim, mode);
 
        hrtimer_set_expires_range_ns(timer, tim, delta_ns);
 
@@ -1074,19 +1081,23 @@ EXPORT_SYMBOL_GPL(hrtimer_cancel);
 /**
  * hrtimer_get_remaining - get remaining time for the timer
  * @timer:     the timer to read
+ * @adjust:    adjust relative timers when CONFIG_TIME_LOW_RES=y
  */
-ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
+ktime_t __hrtimer_get_remaining(const struct hrtimer *timer, bool adjust)
 {
        unsigned long flags;
        ktime_t rem;
 
        lock_hrtimer_base(timer, &flags);
-       rem = hrtimer_expires_remaining(timer);
+       if (IS_ENABLED(CONFIG_TIME_LOW_RES) && adjust)
+               rem = hrtimer_expires_remaining_adjusted(timer);
+       else
+               rem = hrtimer_expires_remaining(timer);
        unlock_hrtimer_base(timer, &flags);
 
        return rem;
 }
-EXPORT_SYMBOL_GPL(hrtimer_get_remaining);
+EXPORT_SYMBOL_GPL(__hrtimer_get_remaining);
 
 #ifdef CONFIG_NO_HZ_COMMON
 /**
@@ -1219,6 +1230,14 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
        timer_stats_account_hrtimer(timer);
        fn = timer->function;
 
+       /*
+        * Clear the 'is relative' flag for the TIME_LOW_RES case. If the
+        * timer is restarted with a period then it becomes an absolute
+        * timer. If its not restarted it does not matter.
+        */
+       if (IS_ENABLED(CONFIG_TIME_LOW_RES))
+               timer->is_rel = false;
+
        /*
         * Because we run timers from hardirq context, there is no chance
         * they get migrated to another cpu, therefore its safe to unlock

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index f75e35b6014900da71ffa438a507c34f19e36e3a..ba7d8b288bb37250ce9e9c0e5f562b45832c4ca9 100644 (file)
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -69,7 +69,7 @@ print_timer(struct seq_file *m, struct hrtimer *taddr, struct hrtimer *timer,
        print_name_offset(m, taddr);
        SEQ_printf(m, ", ");
        print_name_offset(m, timer->function);
-       SEQ_printf(m, ", S:%02lx", timer->state);
+       SEQ_printf(m, ", S:%02x", timer->state);
 #ifdef CONFIG_TIMER_STATS
        SEQ_printf(m, ", ");
        print_name_offset(m, timer->start_site);