From: Nicholas Piggin npiggin@gmail.com
commit 5d5e4522a7f404d1a96fd6c703989d32a9c9568d upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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(+)
--- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -187,6 +187,12 @@ static void watchdog_smp_panic(int cpu, 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");
--- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -198,6 +198,7 @@ void dump_stack_print_info(const char *l 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) @@ -274,6 +275,9 @@ static inline void dump_stack_lvl(const static inline void dump_stack(void) { } +static inline void printk_trigger_flush(void) +{ +} #endif
#ifdef CONFIG_SMP --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3252,6 +3252,11 @@ 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; --- a/lib/nmi_backtrace.c +++ b/lib/nmi_backtrace.c @@ -75,6 +75,12 @@ void nmi_trigger_cpumask_backtrace(const 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(); }