From: Nicholas Piggin Date: Sun, 7 Nov 2021 04:51:16 +0000 (+1000) Subject: printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces X-Git-Tag: Ubuntu-5.15.0-16.16~1029 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=1bb8bf05aae209226ee8b8fb2829da37f3878f26;p=mirror_ubuntu-jammy-kernel.git printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces BugLink: https://bugs.launchpad.net/bugs/1952579 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 Reviewed-by: Petr Mladek Reviewed-by: John Ogness Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20211107045116.1754411-1-npiggin@gmail.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Andrea Righi --- diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index f9ea0e5357f9..3fa6d240bade 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -187,6 +187,12 @@ 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 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(); }