Re: [PATCH v5] printk: hash addresses printed with %p

[Jason A. Donenfeld]

On Thu, Oct 19, 2017 at 3:31 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@xxxxxxxxx> wrote:
> On (10/19/17 03:03), Jason A. Donenfeld wrote:
> [..]
>> 1) Go back to the spinlock yourself.
>
> so we ruled out NMI deadlocks?

Oh, right. No, I haven't thought through this enough to rule it out.
Indeed if that's an issue, the locks in the _once code will also be an
issue.

So if locking is totally impossible, then a race-free way of doing
this is with a tri-state compare and exchange. Things are either: in
state 1: no key, state 2: getting key, state 3: have key. If state 1
or 2, print the placeholder token. If state 3, do the hashing.