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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2015-03-16 15:54:29 -0400
committerAnders Roxell <anders.roxell@linaro.org>2015-06-01 12:03:39 +0200
commitea60c8a4d0c5f0ad17fcf77032c8e86c18c41a2c (patch)
tree634f5e1fc3a8b4c6371d060ad0afb78bebcf4490
parent53be47e5c1fa3b4edce74a21771c6008163e91ab (diff)
downloadlinux-linaro-stable-ea60c8a4d0c5f0ad17fcf77032c8e86c18c41a2c.tar.gz
Revert "timers: do not raise softirq unconditionally"
This reverts commit 891f510568343d93c5aa2f477b6bebe009b48f05. An issue arisen that if a rt_mutex (spin_lock converted to a mutex in PREEMPT_RT) is taken in hard interrupt context, it could cause a false deadlock detection and trigger a BUG_ON() from the return value of task_blocks_on_rt_mutex() in rt_spin_lock_slowlock(). The problem is this: CPU0 CPU1 ---- ---- spin_lock(A) spin_lock(A) [ blocks, but spins as owner on CPU 0 is running ] <interrupt> spin_trylock(B) [ succeeds ] spin_lock(B) <blocks> Now the deadlock detection triggers and follows the locking: Task X (on CPU0) blocked on spinlock B owned by task Y on CPU1 (via the interrupt taking it with a try lock) The owner of B (Y) is blocked on spin_lock A (still spinning) A is owned by task X (self). DEADLOCK detected! BUG_ON triggered. This was caused by the code to try to not raise softirq unconditionally to allow NO_HZ_FULL to work. Unfortunately, reverting that patch causes NO_HZ_FULL to break again, but that's still better than triggering a BUG_ON(). Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Conflicts: kernel/timer.c
-rw-r--r--include/linux/hrtimer.h3
-rw-r--r--kernel/hrtimer.c31
-rw-r--r--kernel/timer.c46
3 files changed, 28 insertions, 52 deletions
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index bdbf77db0f4d..79a7a35e1a6e 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -461,8 +461,9 @@ extern int schedule_hrtimeout_range_clock(ktime_t *expires,
unsigned long delta, const enum hrtimer_mode mode, int clock);
extern int schedule_hrtimeout(ktime_t *expires, const enum hrtimer_mode mode);
-/* Called from the periodic timer tick */
+/* Soft interrupt function to run the hrtimer queues: */
extern void hrtimer_run_queues(void);
+extern void hrtimer_run_pending(void);
/* Bootup initialization: */
extern void __init hrtimers_init(void);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index f97b9f65c5fa..164201aba52f 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1717,6 +1717,30 @@ static void run_hrtimer_softirq(struct softirq_action *h)
}
/*
+ * Called from timer softirq every jiffy, expire hrtimers:
+ *
+ * For HRT its the fall back code to run the softirq in the timer
+ * softirq context in case the hrtimer initialization failed or has
+ * not been done yet.
+ */
+void hrtimer_run_pending(void)
+{
+ if (hrtimer_hres_active())
+ return;
+
+ /*
+ * This _is_ ugly: We have to check in the softirq context,
+ * whether we can switch to highres and / or nohz mode. The
+ * clocksource switch happens in the timer interrupt with
+ * xtime_lock held. Notification from there only sets the
+ * check bit in the tick_oneshot code, otherwise we might
+ * deadlock vs. xtime_lock.
+ */
+ if (tick_check_oneshot_change(!hrtimer_is_hres_enabled()))
+ hrtimer_switch_to_hres();
+}
+
+/*
* Called from hardirq context every jiffy
*/
void hrtimer_run_queues(void)
@@ -1729,13 +1753,6 @@ void hrtimer_run_queues(void)
if (hrtimer_hres_active())
return;
- /*
- * Check whether we can switch to highres mode.
- */
- if (tick_check_oneshot_change(!hrtimer_is_hres_enabled())
- && hrtimer_switch_to_hres())
- return;
-
for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
base = &cpu_base->clock_base[index];
if (!timerqueue_getnext(&base->active))
diff --git a/kernel/timer.c b/kernel/timer.c
index 2059f6b27595..34fd2dbba3e3 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1464,6 +1464,8 @@ static void run_timer_softirq(struct softirq_action *h)
{
struct tvec_base *base = __this_cpu_read(tvec_bases);
+ hrtimer_run_pending();
+
#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
irq_work_run();
#endif
@@ -1477,52 +1479,8 @@ static void run_timer_softirq(struct softirq_action *h)
*/
void run_local_timers(void)
{
- struct tvec_base *base = __this_cpu_read(tvec_bases);
-
hrtimer_run_queues();
- /*
- * We can access this lockless as we are in the timer
- * interrupt. If there are no timers queued, nothing to do in
- * the timer softirq.
- */
-#ifdef CONFIG_PREEMPT_RT_FULL
-
-#ifndef CONFIG_SMP
- /*
- * The spin_do_trylock() later may fail as the lock may be hold before
- * the interrupt arrived. The spin-lock debugging code will raise a
- * warning if the try_lock fails on UP. Since this is only an
- * optimization for the FULL_NO_HZ case (not to run the timer softirq on
- * an nohz_full CPU) we don't really care and shedule the softirq.
- */
raise_softirq(TIMER_SOFTIRQ);
- return;
-#endif
-
- /* On RT, irq work runs from softirq */
- if (irq_work_needs_cpu()) {
- raise_softirq(TIMER_SOFTIRQ);
- return;
- }
-
- if (!spin_do_trylock(&base->lock)) {
- raise_softirq(TIMER_SOFTIRQ);
- return;
- }
-#endif
-
- if (!base->active_timers)
- goto out;
-
- /* Check whether the next pending timer has expired */
- if (time_before_eq(base->next_timer, jiffies))
- raise_softirq(TIMER_SOFTIRQ);
-out:
-#ifdef CONFIG_PREEMPT_RT_FULL
- rt_spin_unlock_after_trylock_in_irq(&base->lock);
-#endif
- /* The ; ensures that gcc won't complain in the !RT case */
- ;
}
#ifdef __ARCH_WANT_SYS_ALARM