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
|
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 22 Jul 2011 17:58:40 +0200
Subject: [PATCH 057/354] printk: Add a printk kill switch
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=3b0bd8c73adefa7c822cad0561539e02ed4dcf25
Add a prinkt-kill-switch. This is used from (NMI) watchdog to ensure that
it does not dead-lock with the early printk code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/printk.h | 2 ++
kernel/printk/printk.c | 79 +++++++++++++++++++++++++++++++-----------
kernel/watchdog_hld.c | 10 ++++++
3 files changed, 71 insertions(+), 20 deletions(-)
diff --git a/include/linux/printk.h b/include/linux/printk.h
index f4d7e643f010..586be4c5df96 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -140,9 +140,11 @@ struct va_format {
#ifdef CONFIG_EARLY_PRINTK
extern asmlinkage __printf(1, 2)
void early_printk(const char *fmt, ...);
+extern void printk_kill(void);
#else
static inline __printf(1, 2) __cold
void early_printk(const char *s, ...) { }
+static inline void printk_kill(void) { }
#endif
#ifdef CONFIG_PRINTK_NMI
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2ba16c426ba5..963c20ab9548 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -407,6 +407,58 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
printk_safe_exit_irqrestore(flags); \
} while (0)
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+static void early_vprintk(const char *fmt, va_list ap)
+{
+ if (early_console) {
+ char buf[512];
+ int n = vscnprintf(buf, sizeof(buf), fmt, ap);
+
+ early_console->write(early_console, buf, n);
+ }
+}
+
+asmlinkage void early_printk(const char *fmt, ...)
+{
+ va_list ap;
+
+ va_start(ap, fmt);
+ early_vprintk(fmt, ap);
+ va_end(ap);
+}
+
+/*
+ * This is independent of any log levels - a global
+ * kill switch that turns off all of printk.
+ *
+ * Used by the NMI watchdog if early-printk is enabled.
+ */
+static bool __read_mostly printk_killswitch;
+
+void printk_kill(void)
+{
+ printk_killswitch = true;
+}
+
+#ifdef CONFIG_PRINTK
+static int forced_early_printk(const char *fmt, va_list ap)
+{
+ if (!printk_killswitch)
+ return 0;
+ early_vprintk(fmt, ap);
+ return 1;
+}
+#endif
+
+#else
+static inline int forced_early_printk(const char *fmt, va_list ap)
+{
+ return 0;
+}
+#endif
+
#ifdef CONFIG_PRINTK
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* the next printk record to read by syslog(READ) or /proc/kmsg */
@@ -1935,6 +1987,13 @@ asmlinkage int vprintk_emit(int facility, int level,
unsigned long flags;
u64 curr_log_seq;
+ /*
+ * Fall back to early_printk if a debugging subsystem has
+ * killed printk output
+ */
+ if (unlikely(forced_early_printk(fmt, args)))
+ return 1;
+
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
in_sched = true;
@@ -2079,26 +2138,6 @@ static bool suppress_message_printing(int level) { return false; }
#endif /* CONFIG_PRINTK */
-#ifdef CONFIG_EARLY_PRINTK
-struct console *early_console;
-
-asmlinkage __visible void early_printk(const char *fmt, ...)
-{
- va_list ap;
- char buf[512];
- int n;
-
- if (!early_console)
- return;
-
- va_start(ap, fmt);
- n = vscnprintf(buf, sizeof(buf), fmt, ap);
- va_end(ap);
-
- early_console->write(early_console, buf, n);
-}
-#endif
-
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options)
{
diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index f8e460b4a59d..72a119b97f3e 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -24,6 +24,8 @@ static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
static DEFINE_PER_CPU(struct perf_event *, dead_event);
+static DEFINE_RAW_SPINLOCK(watchdog_output_lock);
+
static struct cpumask dead_events_mask;
static unsigned long hardlockup_allcpu_dumped;
@@ -134,6 +136,13 @@ static void watchdog_overflow_callback(struct perf_event *event,
/* only print hardlockups once */
if (__this_cpu_read(hard_watchdog_warn) == true)
return;
+ /*
+ * If early-printk is enabled then make sure we do not
+ * lock up in printk() and kill console logging:
+ */
+ printk_kill();
+
+ raw_spin_lock(&watchdog_output_lock);
pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
print_modules();
@@ -151,6 +160,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
!test_and_set_bit(0, &hardlockup_allcpu_dumped))
trigger_allbutself_cpu_backtrace();
+ raw_spin_unlock(&watchdog_output_lock);
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
|
