178 lines
4.9 KiB
Diff
178 lines
4.9 KiB
Diff
From 63e0e7b2d6fd6bf9ec8e39c77fd05349fc6f5833 Mon Sep 17 00:00:00 2001
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Message-Id: <63e0e7b2d6fd6bf9ec8e39c77fd05349fc6f5833.1601675151.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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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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Subject: [PATCH 057/333] printk: Add a printk kill switch
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.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_hld.c | 10 ++++++
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3 files changed, 71 insertions(+), 20 deletions(-)
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diff --git a/include/linux/printk.h b/include/linux/printk.h
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index 6dd867e39365..b9d050428456 100644
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--- a/include/linux/printk.h
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+++ b/include/linux/printk.h
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@@ -140,9 +140,11 @@ 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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diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
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index 3cb0e5b479ff..e14732bd316f 100644
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -405,6 +405,58 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
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printk_safe_exit_irqrestore(flags); \
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} while (0)
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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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@@ -1933,6 +1985,13 @@ asmlinkage int vprintk_emit(int facility, int level,
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unsigned long flags;
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u64 curr_log_seq;
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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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@@ -2077,26 +2136,6 @@ static bool suppress_message_printing(int level) { return false; }
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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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diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
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index 71381168dede..685443375dc0 100644
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--- a/kernel/watchdog_hld.c
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+++ b/kernel/watchdog_hld.c
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@@ -24,6 +24,8 @@ static DEFINE_PER_CPU(bool, hard_watchdog_warn);
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static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
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static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
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static DEFINE_PER_CPU(struct perf_event *, dead_event);
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+static DEFINE_RAW_SPINLOCK(watchdog_output_lock);
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+
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static struct cpumask dead_events_mask;
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static unsigned long hardlockup_allcpu_dumped;
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@@ -134,6 +136,13 @@ static void watchdog_overflow_callback(struct perf_event *event,
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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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@@ -151,6 +160,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
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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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--
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2.17.1
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