[dm-devel] Serial console is causing system lock-up

[Sergey Senozhatsky]

On (03/06/19 23:43), John Ogness wrote:
> > Sounds like another aurgment for the new printk design.
> 
> Assuming the bad checksum messages are considered an emergency (for
> example, at least loglevel KERN_WARN), then the new printk design would
> print those messages synchronously to the slow serial line in the
> context of the driver as the driver is producing them.

I wonder if we have several CPU doing the checksum verification.
New sync printk mechanism has a Big-Konsole-spin-Lock, all CPUs that
want to printk() should line up and wait, in whatever context they
currently are.

> There wouldn't be a lock-up, but it would definitely slow down the
> driver. The situation of "messages being produced faster than the kernel
> can write them" would never exist because the printk() call will only
> return after the writing is completed.

If the serial console is a really slow one and we have a CPU in atomic
context spinnig on prb_lock, while the prb_lock is always acquired by
other CPUs, then it may look like a lock-up scenario.

	-ss