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author | john stultz <johnstul@us.ibm.com> | 2009-05-01 13:10:25 -0700 |
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committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-05-08 14:54:36 -0700 |
commit | 2ee201a9d57df7a12e228c6a9b06a15014231b72 (patch) | |
tree | 9c838f6bcfaafb1e0f932a9d7a8ba42e18921dc8 | |
parent | 070bb0f3b6df167554f0ecdeb17a5bcdb1cd7b83 (diff) | |
download | lwn-2ee201a9d57df7a12e228c6a9b06a15014231b72.tar.gz lwn-2ee201a9d57df7a12e228c6a9b06a15014231b72.zip |
clockevents: prevent endless loop in tick_handle_periodic()
commit 74a03b69d1b5ce00a568e142ca97e76b7f5239c6 upstream.
tick_handle_periodic() can lock up hard when a one shot clock event
device is used in combination with jiffies clocksource.
Avoid an endless loop issue by requiring that a highres valid
clocksource be installed before we call tick_periodic() in a loop when
using ONESHOT mode. The result is we will only increment jiffies once
per interrupt until a continuous hardware clocksource is available.
Without this, we can run into a endless loop, where each cycle through
the loop, jiffies is updated which increments time by tick_period or
more (due to clock steering), which can cause the event programming to
think the next event was before the newly incremented time and fail
causing tick_periodic() to be called again and the whole process loops
forever.
[ Impact: prevent hard lock up ]
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | kernel/time/tick-common.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index df12434b43ca..bad22e2a5523 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -93,7 +93,17 @@ void tick_handle_periodic(struct clock_event_device *dev) for (;;) { if (!clockevents_program_event(dev, next, ktime_get())) return; - tick_periodic(cpu); + /* + * Have to be careful here. If we're in oneshot mode, + * before we call tick_periodic() in a loop, we need + * to be sure we're using a real hardware clocksource. + * Otherwise we could get trapped in an infinite + * loop, as the tick_periodic() increments jiffies, + * when then will increment time, posibly causing + * the loop to trigger again and again. + */ + if (timekeeping_valid_for_hres()) + tick_periodic(cpu); next = ktime_add(next, tick_period); } } |