linux-kernel - Re: [PATCH v5 1/4] printk/nmi: generic solution for safe printk in NMI

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Date:   Fri, 28 Apr 2017 10:25:30 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jiri Kosina <jkosina@...e.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Chris Metcalf <cmetcalf@...hip.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-cris-kernel@...s.com, linux-mips@...ux-mips.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Ralf Baechle <ralf@...ux-mips.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH v5 1/4] printk/nmi: generic solution for safe printk in
 NMI


On (04/20/17 15:11), Petr Mladek wrote:
[..]
>  void printk_nmi_enter(void)
>  {
> -	this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
> +	/*
> +	 * The size of the extra per-CPU buffer is limited. Use it
> +	 * only when really needed.
> +	 */
> +	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK ||
> +	    raw_spin_is_locked(&logbuf_lock)) {

can we please have && here?


[..]
> diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
> index 4e8a30d1c22f..0bc0a3535a8a 100644
> --- a/lib/nmi_backtrace.c
> +++ b/lib/nmi_backtrace.c
> @@ -86,9 +86,11 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
>  
>  bool nmi_cpu_backtrace(struct pt_regs *regs)
>  {
> +	static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED;
>  	int cpu = smp_processor_id();
>  
>  	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
> +		arch_spin_lock(&lock);
>  		if (regs && cpu_in_idle(instruction_pointer(regs))) {
>  			pr_warn("NMI backtrace for cpu %d skipped: idling at pc %#lx\n",
>  				cpu, instruction_pointer(regs));
> @@ -99,6 +101,7 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
>  			else
>  				dump_stack();
>  		}
> +		arch_spin_unlock(&lock);
>  		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
>  		return true;
>  	}

can the nmi_backtrace part be a patch on its own?

	-ss