Messages in this thread | | | From | John Ogness <> | Subject | Re: [PATCH] printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces | Date | Mon, 08 Nov 2021 11:46:13 +0106 |
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On 2021-11-07, Nicholas Piggin <npiggin@gmail.com> wrote: > 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") > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
> --- > 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 5f69ba4de1f3..c8017bc23b00 100644 > --- a/arch/powerpc/kernel/watchdog.c > +++ b/arch/powerpc/kernel/watchdog.c > @@ -227,6 +227,12 @@ static void watchdog_smp_panic(int cpu) > cpumask_clear(&wd_smp_cpus_ipi); > } > > + /* > + * 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 85b656f82d75..9497f6b98339 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -198,6 +198,7 @@ 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) > @@ -274,6 +275,9 @@ 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 a8d0a58deebc..99221b016c68 100644 > --- 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; > 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(); > } > -- > 2.23.0
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