clockevents: Prevent oneshot mode when broadcast device is periodic

When the per cpu timer is marked CLOCK_EVT_FEAT_C3STOP, then we only
can switch into oneshot mode, when the backup broadcast device
supports oneshot mode as well. Otherwise we would try to switch the
broadcast device into an unsupported mode unconditionally. This went
unnoticed so far as the current available broadcast devices support
oneshot mode. Seth unearthed this problem while debugging and working
around an hpet related BIOS wreckage.

Add the necessary check to tick_is_oneshot_available().

Reported-and-tested-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <alpine.LFD.2.00.1102252231200.2701@localhost6.localdomain6>
Cc: stable@kernel.org # .21 ->

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 48b2761b5668119bc932b6278289bf8a481be050..a3b5aff626064fa153771f03b3f53743459cfc32 100644 (file)
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -600,4 +600,14 @@ int tick_broadcast_oneshot_active(void)
        return tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT;
 }
 
+/*
+ * Check whether the broadcast device supports oneshot.
+ */
+bool tick_broadcast_oneshot_available(void)
+{
+       struct clock_event_device *bc = tick_broadcast_device.evtdev;
+
+       return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;
+}
+
 #endif

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 051bc80a0c435cf47a8dfb8a0f5d2d49d20e188c..ed228ef6f6b8dc80932cf76e79254dd509d0708d 100644 (file)
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -51,7 +51,11 @@ int tick_is_oneshot_available(void)
 {
        struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 
-       return dev && (dev->features & CLOCK_EVT_FEAT_ONESHOT);
+       if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
+               return 0;
+       if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
+               return 1;
+       return tick_broadcast_oneshot_available();
 }
 
 /*

diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 290eefbc1f608ec4d9c957fb5798eb53490f9e7c..f65d3a723a6423d6882f0169251173d16af81921 100644 (file)
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -36,6 +36,7 @@ extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
 extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
 extern int tick_broadcast_oneshot_active(void);
 extern void tick_check_oneshot_broadcast(int cpu);
+bool tick_broadcast_oneshot_available(void);
 # else /* BROADCAST */
 static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 {
@@ -46,6 +47,7 @@ static inline void tick_broadcast_switch_to_oneshot(void) { }
 static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
 static inline int tick_broadcast_oneshot_active(void) { return 0; }
 static inline void tick_check_oneshot_broadcast(int cpu) { }
+static inline bool tick_broadcast_oneshot_available(void) { return true; }
 # endif /* !BROADCAST */
 
 #else /* !ONESHOT */
@@ -76,6 +78,7 @@ static inline int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
        return 0;
 }
 static inline int tick_broadcast_oneshot_active(void) { return 0; }
+static inline bool tick_broadcast_oneshot_available(void) { return false; }
 #endif /* !TICK_ONESHOT */
 
 /*