[BUG] genpd: domains can suspend asynchronously

[Brian Norris <briannorris@chromium.org>]

Hi,

I reported this previously in the midst of another tangentially-related
thread, so it could easily have gotten lost. I thought I'd repeat it
here.

---

I noticed the genpd code has comments like this scattered all over:

 * This function is only called in "noirq" and "syscore" stages of system power
 * transitions, so it need not acquire locks (all of the "noirq" callbacks are
 * executed sequentially, so it is guaranteed that it will never run twice in
 * parallel).

Isn't that no longer true, now that noirq suspend can be asynchronous?
Maybe we should grep for the phrase "need not acquire locks" throughout
the kernel, in order to find low-hanging fruit for race conditions :)

---

Anyway, I was considering hacking my way through the subsystem here
sometime, but there's no guarantee. And in case someone else wanted to
fix this up, I figured I'd least put the report out there.

NB: I noticed there are more drivers enabling asynchronous suspend these
days. Some USB, SDIO, and MMC host controllers seem ripe for triggering
bugs here.

Brian