[PATCHv4 1/4] nvme: Sync request queues on reset

[keith.busch@linux.intel.com (Keith Busch)]

On Mon, Jul 16, 2018@05:51:47PM +0300, Sagi Grimberg wrote:
> Keith,
> 
> > This patch fixes races that occur with simultaneous controller
> > resets by synchronizing request queues prior to initializing the
> > controller. Withouth this, a thread may attempt disabling a controller
> > at the same time as we're trying to enable it.
> 
> I'll need a little more help with this. This is due to the
> fact that we disable the controller directly from the timeout
> handler? If not, what context may disable when nvme_reset_work
> is running?
> 
> I'm trying what the sync should serialize and why is it not
> serialized by the controller state machine.

The only reason we need this is because each namespace has its own
request queue with their own timeout work. We don't want all of these
scheduling multiple controller resets, so the sync here just ensures
that there is no active timeout work that's about to schedule another
reset while we're already resetting the controller.