Messages in this thread | | | Date | Thu, 31 Mar 2022 10:57:40 -0600 | Subject | Re: [PATCH v1 1/3] driver core: Support asynchronous driver shutdown | From | Jonathan Derrick <> |
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On 3/28/2022 6:19 PM, Oliver O'Halloran wrote: > On Tue, Mar 29, 2022 at 10:35 AM Tanjore Suresh <tansuresh@google.com> wrote: >> >> This changes the bus driver interface with additional entry points >> to enable devices to implement asynchronous shutdown. The existing >> synchronous interface to shutdown is unmodified and retained for >> backward compatibility. >> >> This changes the common device shutdown code to enable devices to >> participate in asynchronous shutdown implementation. > > nice to see someone looking at improving the shutdown path > >> Signed-off-by: Tanjore Suresh <tansuresh@google.com> >> --- >> drivers/base/core.c | 39 +++++++++++++++++++++++++++++++++++++- >> include/linux/device/bus.h | 10 ++++++++++ >> 2 files changed, 48 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/base/core.c b/drivers/base/core.c >> index 3d6430eb0c6a..359e7067e8b8 100644 >> --- a/drivers/base/core.c >> +++ b/drivers/base/core.c >> @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); >> *snip* > > This all seems a bit dangerous and I'm wondering what systems you've > tested these changes with. I had a look at implementing something > similar a few years ago and one case that always concerned me was > embedded systems where the PCIe root complex also has a driver bound. > Say you've got the following PCIe topology: > > 00:00.0 - root port > 01:00.0 - nvme drive > > With the current implementation of device_shutdown() we can guarantee > that the child device (the nvme) is shut down before we start trying > to shut down the parent device (the root complex) so there's no > possibility of deadlocks and other dependency headaches. With this > implementation of async shutdown we lose that guarantee and I'm not > sure what the consequences are. Personally I was never able to > convince myself it was safe, but maybe you're braver than I am :) > > That all said, there's probably only a few kinds of device that will > really want to implement async shutdown support so maybe you can > restrict it to leaf devices and flip the ordering around to something > like:
It seems like it might be helpful to split the async shutdowns into refcounted hierarchies and proceed with the next level up when all the refs are in.
Ex: 00:00.0 - RP 01:00.0 - NVMe A 02:00.0 - Bridge USP 03:00.0 - Bridge DSP 04:00.0 - NVMe B 03:00.1 - Bridge DSP 05:00.0 - NVMe C
NVMe A could start shutting down at the beginning of the hierarchy traversal. Then async shutdown of bus 3 wouldn't start until all children of bus 3 are shutdown.
You could probably do this by having the async_shutdown_list in the pci_bus.
> > for_each_device(dev) { > if (can_async(dev) && has_no_children(dev)) > start_async_shutdown(dev) > } > wait_for_all_async_shutdowns_to_finish() > > // tear down the remaining system devices synchronously > for_each_device(dev) > do_sync_shutdown(dev) > >> /* >> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h >> index a039ab809753..e261819601e9 100644 >> --- a/include/linux/device/bus.h >> +++ b/include/linux/device/bus.h >> @@ -93,6 +101,8 @@ struct bus_type { >> void (*sync_state)(struct device *dev); >> void (*remove)(struct device *dev); >> void (*shutdown)(struct device *dev); >> + void (*shutdown_pre)(struct device *dev); >> + void (*shutdown_post)(struct device *dev); > > Call them shutdown_async_start() / shutdown_async_end() or something > IMO. These names are not at all helpful and they're easy to mix up > their role with the class based shutdown_pre / _post >
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