Re: [PATCH] printk/nmi: Prevent deadlock when serializing NMI backtraces

On (05/22/18 17:43), Steven Rostedt wrote:

...

CPU0 CPU1 CPU2

printk() vprintk_emit() spin_lock(&logbuf_lock)

				trigger_all_cpu_backtrace()
				  raise()

	nmi_enter()
	  printk_nmi_enter()
	    if (this_cpu_read(printk_context)
	      & PRINTK_SAFE_CONTEXT_MASK)
	      // false
	    else
	      // looks safe to use printk_deferred()
	      this_cpu_or(printk_context,
		PRINTK_NMI_DEFERRED_CONTEXT_MASK);

	  nmi_cpu_backtrace()
	    arch_spin_lock(&lock);

What branch is this based on, because I can't find the "arch_spin_lock()" you are talking about here.

This arch_spin_lock() is in lib/nmi_backtrace.c

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/...

-ss