1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
|
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:29:34 -0500
Subject: [PATCH 089/342] timers: Prepare for full preemption
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=6e530eb3ecf4c019b3d4a2b5f00c0dcd295c741f
When softirqs can be preempted we need to make sure that cancelling
the timer from the active thread can not deadlock vs. a running timer
callback. Add a waitqueue to resolve that.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/timer.h | 2 +-
kernel/sched/core.c | 9 +++++++--
kernel/time/timer.c | 45 +++++++++++++++++++++++++++++++++++++++----
3 files changed, 49 insertions(+), 7 deletions(-)
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 7b066fd38248..54627d046b3a 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -172,7 +172,7 @@ extern void add_timer(struct timer_list *timer);
extern int try_to_del_timer_sync(struct timer_list *timer);
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
extern int del_timer_sync(struct timer_list *timer);
#else
# define del_timer_sync(t) del_timer(t)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0a51a66f5a63..974d92afd23e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -498,11 +498,14 @@ void resched_cpu(int cpu)
*/
int get_nohz_timer_target(void)
{
- int i, cpu = smp_processor_id();
+ int i, cpu;
struct sched_domain *sd;
+ preempt_disable_rt();
+ cpu = smp_processor_id();
+
if (!idle_cpu(cpu) && housekeeping_cpu(cpu, HK_FLAG_TIMER))
- return cpu;
+ goto preempt_en_rt;
rcu_read_lock();
for_each_domain(cpu, sd) {
@@ -521,6 +524,8 @@ int get_nohz_timer_target(void)
cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
unlock:
rcu_read_unlock();
+preempt_en_rt:
+ preempt_enable_rt();
return cpu;
}
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a6e88d9bb931..0043bf8e2c90 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -45,6 +45,7 @@
#include <linux/slab.h>
#include <linux/compat.h>
#include <linux/random.h>
+#include <linux/swait.h>
#include <linux/uaccess.h>
#include <asm/unistd.h>
@@ -198,6 +199,9 @@ EXPORT_SYMBOL(jiffies_64);
struct timer_base {
raw_spinlock_t lock;
struct timer_list *running_timer;
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct swait_queue_head wait_for_running_timer;
+#endif
unsigned long clk;
unsigned long next_expiry;
unsigned int cpu;
@@ -1190,6 +1194,33 @@ void add_timer_on(struct timer_list *timer, int cpu)
}
EXPORT_SYMBOL_GPL(add_timer_on);
+#ifdef CONFIG_PREEMPT_RT_FULL
+/*
+ * Wait for a running timer
+ */
+static void wait_for_running_timer(struct timer_list *timer)
+{
+ struct timer_base *base;
+ u32 tf = timer->flags;
+
+ if (tf & TIMER_MIGRATING)
+ return;
+
+ base = get_timer_base(tf);
+ swait_event_exclusive(base->wait_for_running_timer,
+ base->running_timer != timer);
+}
+
+# define wakeup_timer_waiters(b) swake_up_all(&(b)->wait_for_running_timer)
+#else
+static inline void wait_for_running_timer(struct timer_list *timer)
+{
+ cpu_relax();
+}
+
+# define wakeup_timer_waiters(b) do { } while (0)
+#endif
+
/**
* del_timer - deactivate a timer.
* @timer: the timer to be deactivated
@@ -1245,7 +1276,7 @@ int try_to_del_timer_sync(struct timer_list *timer)
}
EXPORT_SYMBOL(try_to_del_timer_sync);
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
/**
* del_timer_sync - deactivate a timer and wait for the handler to finish.
* @timer: the timer to be deactivated
@@ -1305,7 +1336,7 @@ int del_timer_sync(struct timer_list *timer)
int ret = try_to_del_timer_sync(timer);
if (ret >= 0)
return ret;
- cpu_relax();
+ wait_for_running_timer(timer);
}
}
EXPORT_SYMBOL(del_timer_sync);
@@ -1366,13 +1397,16 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
fn = timer->function;
- if (timer->flags & TIMER_IRQSAFE) {
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL) &&
+ timer->flags & TIMER_IRQSAFE) {
raw_spin_unlock(&base->lock);
call_timer_fn(timer, fn);
+ base->running_timer = NULL;
raw_spin_lock(&base->lock);
} else {
raw_spin_unlock_irq(&base->lock);
call_timer_fn(timer, fn);
+ base->running_timer = NULL;
raw_spin_lock_irq(&base->lock);
}
}
@@ -1695,8 +1729,8 @@ static inline void __run_timers(struct timer_base *base)
while (levels--)
expire_timers(base, heads + levels);
}
- base->running_timer = NULL;
raw_spin_unlock_irq(&base->lock);
+ wakeup_timer_waiters(base);
}
/*
@@ -1941,6 +1975,9 @@ static void __init init_timer_cpu(int cpu)
base->cpu = cpu;
raw_spin_lock_init(&base->lock);
base->clk = jiffies;
+#ifdef CONFIG_PREEMPT_RT_FULL
+ init_swait_queue_head(&base->wait_for_running_timer);
+#endif
}
}
|
