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authorStuart Hayes <stuart.w.hayes@gmail.com>2014-04-29 17:55:02 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-07 10:28:11 -0700
commit149c874163b1e5f13e46f8a87b1e69fa7b613b92 (patch)
tree5c7a6d9ac561238b85e8e3a0e85b27ea4e0d0aae /kernel
parent1636737609d52bc1560bf8189f4d897c9c8c03f4 (diff)
hrtimer: Prevent all reprogramming if hang detected
commit 6c6c0d5a1c949d2e084706f9e5fb1fccc175b265 upstream. If the last hrtimer interrupt detected a hang it sets hang_detected=1 and programs the clock event device with a delay to let the system make progress. If hang_detected == 1, we prevent reprogramming of the clock event device in hrtimer_reprogram() but not in hrtimer_force_reprogram(). This can lead to the following situation: hrtimer_interrupt() hang_detected = 1; program ce device to Xms from now (hang delay) We have two timers pending: T1 expires 50ms from now T2 expires 5s from now Now T1 gets canceled, which causes hrtimer_force_reprogram() to be invoked, which in turn programs the clock event device to T2 (5 seconds from now). Any hrtimer_start after that will not reprogram the hardware due to hang_detected still being set. So we effectivly block all timers until the T2 event fires and cleans up the hang situation. Add a check for hang_detected to hrtimer_force_reprogram() which prevents the reprogramming of the hang delay in the hardware timer. The subsequent hrtimer_interrupt will resolve all outstanding issues. [ tglx: Rewrote subject and changelog and fixed up the comment in hrtimer_force_reprogram() ] Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com> Link: http://lkml.kernel.org/r/53602DC6.2060101@gmail.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/hrtimer.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 09094361dce5..cdcb926a5445 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -582,6 +582,23 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
cpu_base->expires_next.tv64 = expires_next.tv64;
+ /*
+ * If a hang was detected in the last timer interrupt then we
+ * leave the hang delay active in the hardware. We want the
+ * system to make progress. That also prevents the following
+ * scenario:
+ * T1 expires 50ms from now
+ * T2 expires 5s from now
+ *
+ * T1 is removed, so this code is called and would reprogram
+ * the hardware to 5s from now. Any hrtimer_start after that
+ * will not reprogram the hardware due to hang_detected being
+ * set. So we'd effectivly block all timers until the T2 event
+ * fires.
+ */
+ if (cpu_base->hang_detected)
+ return;
+
if (cpu_base->expires_next.tv64 != KTIME_MAX)
tick_program_event(cpu_base->expires_next, 1);
}