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authorNicholas Piggin <npiggin@gmail.com>2021-11-07 14:51:16 +1000
committerPetr Mladek <pmladek@suse.com>2021-11-10 16:12:00 +0100
commit5d5e4522a7f404d1a96fd6c703989d32a9c9568d (patch)
treef0241bc19c8cc4106ac4d2dff236cd58528ef0e4
parent26d1982fd17c2cac77f9cf764255362ccb28fe49 (diff)
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printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces
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
-rw-r--r--arch/powerpc/kernel/watchdog.c6
-rw-r--r--include/linux/printk.h4
-rw-r--r--kernel/printk/printk.c5
-rw-r--r--lib/nmi_backtrace.c6
4 files changed, 21 insertions, 0 deletions
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();
}