On Wed, May 09, 2018 at 07:57:52AM -0500, Bjorn Helgaas wrote: > On Wed, May 09, 2018 at 01:41:24PM +0200, Lukas Wunner wrote: > > On Fri, Apr 27, 2018 at 02:22:07PM -0500, Bjorn Helgaas wrote: > > > Sinan mooted the idea of using a "no-wait" path of sending the "don't > > > generate hotplug interrupts" command. I think we should work on this > > > idea a little more. If we're shutting down the whole system, I can't > > > believe there's much value in *anything* we do in the pciehp_remove() > > > path. > > > > > > Maybe we should just get rid of pciehp_remove() (and probably > > > pcie_port_remove_service() and the other service driver remove methods) > > > completely. That dates from when the service drivers could be modules that > > > could be potentially unloaded, but unloading them hasn't been possible for > > > years. > > > > Every Thunderbolt device contains a PCIe switch with at least one > > (downstream) hotplug port, so pciehp_remove() is executed on unplug > > of a Thunderbolt device and the assumption that it's unnecessary > > simply because it's builtin isn't correct. > > I agree that simply being builtin isn't a sufficient argument for getting > rid of pciehp_remove(). > > But if we do need pciehp_remove(), we should be able to make a rational > case for why that is. If we're about to turn off the power, it's not > obvious why we would need to deallocate memory, remove sysfs stuff, etc. > If we need to configure the hardware to make it easier for a kexec'd > kernel, that's a possible argument but we should make it explicit. With Thunderbolt, up to 6 devices may be daisy-chained. This means that a hotplug port may have further hotplug ports as (grand-)children. If power is turned off manually via sysfs for a hotplug port, all children (including hotplug ports) are removed by pciehp even though they physically remain attached to the machine. If such removed-in-software-but-physically- still-present devices send an interrupt, and interrupts were not orderly disabled on ->remove, they will be considered spurious interrupts by genirq code. In particular, level-triggered INTx interrupts will immediately lead to an unpleasant user-visible splat and the interrupt will be switched to polling. So there's no way around orderly disabling interrupts in the ->remove path. I agree that ->shutdown is a different story in principle and that disabling devices seems superfluous and counter-intuitive. I imagine kexec might not be the only reason, but also devices passed through to VMs. (What happens if a VM hands a device back to the host in an unclean state on shutdown?) Thanks, Lukas
