From 5d5e4522a7f404d1a96fd6c703989d32a9c9568d Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Sun, 7 Nov 2021 14:51:16 +1000
Subject: [PATCH] printk: restore flushing of NMI buffers on remote CPUs after
NMI backtraces
Git-commit: 5d5e4522a7f404d1a96fd6c703989d32a9c9568d
Patch-mainline: v5.16-rc2
References: bsc#1192988
printk from NMI context relies on irq work being raised on the local CPU
to print to console. This can be a problem if the NMI was raised by a
lockup detector to print lockup stack and regs, because the CPU may not
enable irqs (because it is locked up).
Introduce printk_trigger_flush() that can be called another CPU to try
to get those messages to the console, call that where printk_safe_flush
was previously called.
Fixes: 93d102f094be ("printk: remove safe buffers")
Cc: stable@vger.kernel.org # 5.15
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211107045116.1754411-1-npiggin@gmail.com
---
arch/powerpc/kernel/watchdog.c | 6 ++++++
include/linux/printk.h | 4 ++++
kernel/printk/printk.c | 5 +++++
lib/nmi_backtrace.c | 6 ++++++
4 files changed, 21 insertions(+)
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index dc17d8903d4f..6b7a83d5e03e 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -186,6 +186,12 @@ static void watchdog_smp_panic(int cpu, u64 tb)
if (sysctl_hardlockup_all_cpu_backtrace)
trigger_allbutself_cpu_backtrace();
+ /*
+ * Force flush any remote buffers that might be stuck in IRQ context
+ * and therefore could not run their irq_work.
+ */
+ printk_trigger_flush();
+
if (hardlockup_panic)
nmi_panic(NULL, "Hard LOCKUP");
diff --git a/include/linux/printk.h b/include/linux/printk.h
index a1379df43251..596ad6fa0336 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -206,6 +206,7 @@ void dump_stack_print_info(const char *log_lvl);
void show_regs_print_info(const char *log_lvl);
extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
extern asmlinkage void dump_stack(void) __cold;
+void printk_trigger_flush(void);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@@ -282,6 +283,9 @@ static inline void dump_stack_lvl(const char *log_lvl)
static inline void dump_stack(void)
{
}
+static inline void printk_trigger_flush(void)
+{
+}
#endif
#ifdef CONFIG_SMP
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 65fffa6368c9..eabe23b0a982 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3261,6 +3261,11 @@ void defer_console_output(void)
preempt_enable();
}
+void printk_trigger_flush(void)
+{
+ defer_console_output();
+}
+
int vprintk_deferred(const char *fmt, va_list args)
{
int r;
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index f9e89001b52e..199ab201d501 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -75,6 +75,12 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
touch_softlockup_watchdog();
}
+ /*
+ * Force flush any remote buffers that might be stuck in IRQ context
+ * and therefore could not run their irq_work.
+ */
+ printk_trigger_flush();
+
clear_bit_unlock(0, &backtrace_flag);
put_cpu();
}
--
2.26.2