[PATCH v4 15/13] firmware: arm_sdei: be more robust against cpu-hotplug

On Wed, Nov 08, 2017 at 04:06:24PM +0000, James Morse wrote:

dpm_suspend() calls the freeze/thaw callbacks for hibernate before
disable_non_bootcpus() takes down secondaries.

This leads to a fun race where the freeze/thaw callbacks reset the
SDEI interface (as we may be restoring a kernel with a different
layout due to KASLR), then the cpu-hotplug callbacks come in to
save the current state, which has already been reset.

I tried to solve this with a 'frozen' flag that stops the hotplug
callback from overwriting the saved values. Instead this just
moves the race around and makes it even harder to think about.

Instead, make it look like the secondaries have gone offline.
Call cpuhp_remove_state() in the freeze callback, this will call the
teardown hook on all online CPUs, then remove the state. This saves
all private events and makes future CPU up/down events invisible.

Change sdei_event_unregister_all()/sdei_reregister_events() to
only save/restore shared events, which are all that is left. With
this we can remove the frozen flag. We can remove the device
suspend/resume calls too as cpuhotplug's teardown call has masked
the CPUs.

All that is left is the reboot notifier, (which was abusing the
frozen flag). Call cpuhp_remove_state() to make it look like
secondary CPUs have gone offline.

Suggested-by: Will Deacon <redacted>
Signed-off-by: James Morse <james.morse@arm.com>
---
 drivers/firmware/arm_sdei.c | 60 +++++++++++++++++++++++----------------------
 1 file changed, 31 insertions(+), 29 deletions(-)

Thanks, this appears to address my concerns. It's too late for 4.15 now,
but please resend for 4.16 and Catalin can pick this series up.

Will