Hi Russell,

On Fri, Jun 01, 2018 at 12:00:16PM +0100, Russell King wrote:

Executing loops such as:

	while (1)
		cpu_relax();

with interrupts disabled results in a livelock of the entire system,
as other CPUs are prevented making progress.  This is most noticable
as a failure of crashdump kexec, which stops just after issuing:

	Loading crashdump kernel...

to the system console.  Two other locations of these loops within the
ARM code have been identified and fixed up.

Can you confirm that this only happens if CONFIG_ARM_ERRATA_754327=y?
The only erratum I can find for A9 that matches this behaviour exists
when the body of the tight loop contains a DMB and some of the possible
workarounds are:

  - Add ten NOPs after the DMB
  - Use DSB instead of DMB in the tight loop
  - Set bit 16 in the diagnostic control register (p15, c1, 5, 0, c0, 1)

WFE is probably fine (the write-up isn't clear), but if this only occurs
due to CONFIG_ARM_ERRATA_754327=y it would be nice to mitigate it in the
alternative cpu_relax() definition itself, which isn't generally possible
with WFE.

Will