[PATCH v6 0/4] shut down devices asynchronously

[Stuart Hayes]

This adds the ability for the kernel to shutdown devices asynchronously
(this is V6).

It is in "safe" mode by default (where only devices whose drivers opt-in
are shut down asynchronously), but it can be "on" (where only devices
whose drivers opt-out are shut down synchronously), or "off" (legacy
behavior).

This can dramatically reduce system shutdown/reboot time on systems that
have multiple devices that take many seconds to shut down (like certain
NVMe drives). On one system tested, the shutdown time went from 11 minutes
without this patch to 55 seconds with the patch.

Changes from V5:

Separated into multiple patches to make review easier.
Reworked some code to make it more readable
Made devices wait for consumers to shut down, not just children
  (suggested by David Jeffery)

Changes from V4:

Change code to use cookies for synchronization rather than async domains
Allow async shutdown to be disabled via sysfs, and allow driver opt-in or
  opt-out of async shutdown (when not disabled), with ability to control
  driver opt-in/opt-out via sysfs

Changes from V3:

Bug fix (used "parent" not "dev->parent" in device_shutdown)

Changes from V2:

Removed recursive functions to schedule children to be shutdown before
  parents, since existing device_shutdown loop will already do this

Changes from V1:

Rewritten using kernel async code (suggested by Lukas Wunner)

Stuart Hayes (4):
  driver core: don't always lock parent in shutdown
  driver core: separate function to shutdown one device
  driver core: shut down devices asynchronously
  nvme-pci: Make driver prefer asynchronous shutdown

 drivers/base/base.h           |   3 +
 drivers/base/bus.c            |  47 +++++++++
 drivers/base/core.c           | 185 +++++++++++++++++++++++++++++-----
 drivers/nvme/host/pci.c       |   1 +
 include/linux/device/driver.h |   8 ++
 5 files changed, 218 insertions(+), 26 deletions(-)

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2.39.3