Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"

On (11/01/18 09:05), Daniel Wang wrote:

...

Another deadlock scenario could be the following one:

    printk()
     console_trylock()
      down_trylock()
       raw_spin_lock_irqsave(&sem->lock, flags)
        <NMI>
         panic()
          console_flush_on_panic()
           console_trylock()
            raw_spin_lock_irqsave(&sem->lock, flags)        // deadlock

There are no patches addressing this one at the moment. And it's unclear if you are hitting this scenario.

I am not sure, but Steven's patches did make the deadlock I saw go away...

You certainly can find cases when "busy spin on console_sem owner" logic can reduce some possibilities.

But spin_lock(&lock); NMI; spin_lock(&lock); code is still in the kernel.

A little swamped by other things lately but I'll run a test with it. If it works, would you recommend taking your patch alone

Let's first figure out if it works.

-ss