From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2875C433F5 for ; Mon, 8 Nov 2021 10:40:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A505A61242 for ; Mon, 8 Nov 2021 10:40:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236879AbhKHKnA (ORCPT ); Mon, 8 Nov 2021 05:43:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230310AbhKHKm6 (ORCPT ); Mon, 8 Nov 2021 05:42:58 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CEB66C061570 for ; Mon, 8 Nov 2021 02:40:14 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1636368013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FW6JswIDu9qA1nuRkk62bEsDXrDikiWc8n7F/BGFqE8=; b=0mDUzYRVn4Xk1G+5lUQKnWREAK9xysiSGkWVtXvS5ZScmTlYwMkG8SrUmTJZ66yHNdmK4m ooae4Xb132NKAbEXvmF/3lg91dqsQZmDUZNNclid1bAhSblbAc+guh/cqX1/5nenL0WV0d kE0g9zU16WqNOq5vVCsQqAG0YoNE1tTt76z5+o2pGC+Ne6ekrzk9rFWobwRuQRgS3ue1oz PwTD/fZfYkuAyMcIVKUPsLzslt8wr3OcU6aKUVCGnw821KwIqrkxezlf5XisJ/duVOWvXJ Zw2zdbPQQHpTtwd/rH08vAJHAuypU7EqnpbYZOM3oWbq+KE9g/YPhFX7r2pHPQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1636368013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FW6JswIDu9qA1nuRkk62bEsDXrDikiWc8n7F/BGFqE8=; b=9V/RF8VejtlEIocR6Y/sNvVkp70HyEIsgsNB4SBOFU+0KsNg+/qSHRfQCawhKFResG7xP4 eEsI5hJ0Vc0eRADQ== To: Nicholas Piggin , Petr Mladek Cc: Nicholas Piggin , linux-kernel@vger.kernel.org Subject: Re: [PATCH] printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces In-Reply-To: <20211107045116.1754411-1-npiggin@gmail.com> References: <20211107045116.1754411-1-npiggin@gmail.com> Date: Mon, 08 Nov 2021 11:46:13 +0106 Message-ID: <87cznbx75e.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-11-07, Nicholas Piggin 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 Reviewed-by: John Ogness > --- > 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