Hi Will,

On Fri, Feb 01, 2019 at 10:19:19AM +0000, Will Deacon wrote:

Hi Russell,

On Fri, Jan 25, 2019 at 09:03:57PM +0000, Russell King wrote:

quoted

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.  A workaround for this is to use 10 nops in
cpu_relax().

We also use wfe() in while (1) loops to avoid burning cycles in a
tight loop, giving the CPU a hint that we're not doing anything
useful.

Signed-off-by: Russell King <redacted>
---
It's been a while since this was posted, Will's suggestion was to use
10 nops in cpu_relax() last time around.  I still prefer wfe() in
these infinite-not-doing-anything-ever loops.

 arch/arm/include/asm/barrier.h   | 2 ++
 arch/arm/include/asm/processor.h | 6 +++++-
 arch/arm/kernel/machine_kexec.c  | 5 ++++-
 arch/arm/kernel/smp.c            | 4 +++-
 arch/arm/mach-omap2/prm_common.c | 4 +++-
 5 files changed, 17 insertions(+), 4 deletions(-)

Thanks, this looks good to me and your explanation later in the thread makes
a lot of sense:

Acked-by: Will Deacon <redacted>

Feel free to put some of the erratum writeup that I shared in the commit
message, if you like.

I think it may make more sense to use my writeup as a basis for a
better commit log that explains why we're doing what we're doing.

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