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authorStuart Hayes <stuart.w.hayes@gmail.com>2014-04-29 17:55:02 -0500
committerThomas Gleixner <tglx@linutronix.de>2014-04-30 12:34:51 +0200
commit6c6c0d5a1c949d2e084706f9e5fb1fccc175b265 (patch)
tree997d02e96adcbae3d211c107c567965630b6aa54 /kernel
parentfb0095da19a2e905dfa3141a7704d9614f64992c (diff)
downloadlinux-6c6c0d5a1c949d2e084706f9e5fb1fccc175b265.tar.gz
linux-6c6c0d5a1c949d2e084706f9e5fb1fccc175b265.tar.xz
hrtimer: Prevent all reprogramming if hang detected
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 Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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 d55092c..e3724fd 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -569,6 +569,23 @@ 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);
}