165 lines
4.1 KiB
Diff
165 lines
4.1 KiB
Diff
Subject: printk: Add a printk kill switch
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From: Ingo Molnar <mingo@elte.hu>
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Date: Fri, 22 Jul 2011 17:58:40 +0200
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.8/older/patches-4.8.6-rt5.tar.xz
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Add a prinkt-kill-switch. This is used from (NMI) watchdog to ensure that
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it does not dead-lock with the early printk code.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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include/linux/printk.h | 2 +
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kernel/printk/printk.c | 79 ++++++++++++++++++++++++++++++++++++-------------
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kernel/watchdog.c | 10 ++++++
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3 files changed, 71 insertions(+), 20 deletions(-)
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--- a/include/linux/printk.h
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+++ b/include/linux/printk.h
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@@ -125,9 +125,11 @@ struct va_format {
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#ifdef CONFIG_EARLY_PRINTK
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extern asmlinkage __printf(1, 2)
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void early_printk(const char *fmt, ...);
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+extern void printk_kill(void);
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#else
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static inline __printf(1, 2) __cold
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void early_printk(const char *s, ...) { }
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+static inline void printk_kill(void) { }
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#endif
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#ifdef CONFIG_PRINTK_NMI
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -351,6 +351,58 @@ struct printk_log {
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*/
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DEFINE_RAW_SPINLOCK(logbuf_lock);
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+#ifdef CONFIG_EARLY_PRINTK
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+struct console *early_console;
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+
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+static void early_vprintk(const char *fmt, va_list ap)
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+{
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+ if (early_console) {
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+ char buf[512];
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+ int n = vscnprintf(buf, sizeof(buf), fmt, ap);
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+
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+ early_console->write(early_console, buf, n);
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+ }
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+}
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+
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+asmlinkage void early_printk(const char *fmt, ...)
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+{
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+ va_list ap;
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+
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+ va_start(ap, fmt);
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+ early_vprintk(fmt, ap);
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+ va_end(ap);
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+}
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+
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+/*
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+ * This is independent of any log levels - a global
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+ * kill switch that turns off all of printk.
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+ *
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+ * Used by the NMI watchdog if early-printk is enabled.
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+ */
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+static bool __read_mostly printk_killswitch;
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+
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+void printk_kill(void)
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+{
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+ printk_killswitch = true;
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+}
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+
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+#ifdef CONFIG_PRINTK
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+static int forced_early_printk(const char *fmt, va_list ap)
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+{
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+ if (!printk_killswitch)
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+ return 0;
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+ early_vprintk(fmt, ap);
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+ return 1;
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+}
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+#endif
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+
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+#else
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+static inline int forced_early_printk(const char *fmt, va_list ap)
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+{
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+ return 0;
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+}
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+#endif
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+
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#ifdef CONFIG_PRINTK
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DECLARE_WAIT_QUEUE_HEAD(log_wait);
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/* the next printk record to read by syslog(READ) or /proc/kmsg */
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@@ -1750,6 +1802,13 @@ asmlinkage int vprintk_emit(int facility
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/* cpu currently holding logbuf_lock in this function */
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static unsigned int logbuf_cpu = UINT_MAX;
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+ /*
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+ * Fall back to early_printk if a debugging subsystem has
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+ * killed printk output
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+ */
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+ if (unlikely(forced_early_printk(fmt, args)))
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+ return 1;
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+
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if (level == LOGLEVEL_SCHED) {
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level = LOGLEVEL_DEFAULT;
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in_sched = true;
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@@ -2023,26 +2082,6 @@ DEFINE_PER_CPU(printk_func_t, printk_fun
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#endif /* CONFIG_PRINTK */
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-#ifdef CONFIG_EARLY_PRINTK
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-struct console *early_console;
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-
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-asmlinkage __visible void early_printk(const char *fmt, ...)
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-{
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- va_list ap;
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- char buf[512];
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- int n;
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-
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- if (!early_console)
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- return;
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-
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- va_start(ap, fmt);
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- n = vscnprintf(buf, sizeof(buf), fmt, ap);
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- va_end(ap);
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-
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- early_console->write(early_console, buf, n);
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-}
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-#endif
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-
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static int __add_preferred_console(char *name, int idx, char *options,
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char *brl_options)
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{
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--- a/kernel/watchdog.c
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+++ b/kernel/watchdog.c
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@@ -315,6 +315,8 @@ static int is_softlockup(unsigned long t
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#ifdef CONFIG_HARDLOCKUP_DETECTOR
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+static DEFINE_RAW_SPINLOCK(watchdog_output_lock);
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+
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static struct perf_event_attr wd_hw_attr = {
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.type = PERF_TYPE_HARDWARE,
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.config = PERF_COUNT_HW_CPU_CYCLES,
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@@ -349,6 +351,13 @@ static void watchdog_overflow_callback(s
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/* only print hardlockups once */
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if (__this_cpu_read(hard_watchdog_warn) == true)
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return;
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+ /*
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+ * If early-printk is enabled then make sure we do not
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+ * lock up in printk() and kill console logging:
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+ */
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+ printk_kill();
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+
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+ raw_spin_lock(&watchdog_output_lock);
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pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
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print_modules();
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@@ -366,6 +375,7 @@ static void watchdog_overflow_callback(s
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!test_and_set_bit(0, &hardlockup_allcpu_dumped))
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trigger_allbutself_cpu_backtrace();
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+ raw_spin_unlock(&watchdog_output_lock);
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if (hardlockup_panic)
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nmi_panic(regs, "Hard LOCKUP");
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