On Sat, Jul 04, 2015 at 07:09:19AM -0700, Dan Williams wrote: > On Fri, Jul 3, 2015 at 11:30 AM, Luis R. Rodriguez <[email protected]> wrote: > > On Sat, Jun 27, 2015 at 04:45:25PM -0700, Dan Williams wrote: > >> On Mon, Mar 30, 2015 at 4:20 PM, Dmitry Torokhov > >> <[email protected]> wrote: > >> > Some devices take a long time when initializing, and not all drivers are > >> > suited to initialize their devices when they are open. For example, > >> > input drivers need to interrogate their devices in order to publish > >> > device's capabilities before userspace will open them. When such drivers > >> > are compiled into kernel they may stall entire kernel initialization. > >> > > >> > This change allows drivers request for their probe functions to be > >> > called asynchronously during driver and device registration (manual > >> > binding is still synchronous). Because async_schedule is used to perform > >> > asynchronous calls module loading will still wait for the probing to > >> > complete. > >> > > >> > Note that the end goal is to make the probing asynchronous by default, > >> > so annotating drivers with PROBE_PREFER_ASYNCHRONOUS is a temporary > >> > measure that allows us to speed up boot process while we validating and > >> > fixing the rest of the drivers and preparing userspace. > >> > > >> > This change is based on earlier patch by "Luis R. Rodriguez" > >> > <[email protected]> > >> > > >> > Signed-off-by: Dmitry Torokhov <[email protected]> > >> > --- > >> > drivers/base/base.h | 1 + > >> > drivers/base/bus.c | 31 +++++++--- > >> > drivers/base/dd.c | 149 > >> > ++++++++++++++++++++++++++++++++++++++++++------- > >> > include/linux/device.h | 28 ++++++++++ > >> > 4 files changed, 182 insertions(+), 27 deletions(-) > >> > >> Just noticed this patch. It caught my eye because I had a hard time > >> getting an open coded implementation of asynchronous probing to work > >> in the new libnvdimm subsystem. Especially the messy races of tearing > >> things down while probing is still in flight. I ended up implementing > >> asynchronous device registration which eliminated a lot of complexity > >> and of course the bugs. In general I tend to think that async > >> registration is less risky than async probe since it keeps wider > >> portions of the traditional device model synchronous > > > > but its not see -DEFER_PROBE even before async probe. > > Except in that case you know probe has been seen by the driver at > least once. So I see that as less of a surprise, but point taken. > > >> and leverages the > >> fact that the device model is already well prepared for asynchronous > >> arrival of devices due to hotplug. > > > > I think this sounds reasonable, do you have your code upstream or posted? > > Yes, see nd_device_register() in drivers/nvdimm/bus.c
So no error handling whatsoever, as expected... > > > If not will you be at Plumbers? > > Yes. Me too. > > > Maybe we shoudl talk about this as although > > ChromeOS already likely already jumped on async probe we should address a > > way forward and path forward for other distributions and I don't think > > anyone > > is looking too much into it. async probe came to Linux for two reasons: > > > > * chromeos wanting it > > * an incorrect systemd assumption on how the driver core works > > > > So long term we still need to address the systemd approach, are they going > > to be defaulting now to async probe for all modules? How about for > > built-ins? > > > > We should talk about this and maybe at plumbers. > > > >> Splitting the "initial probe" from > >> the "manual probe" case seems like a recipe for confusion. > > > > If you can come up with pros / cons on both strategies it'd be > > valuable. > > The problem I ran into was needing to remove devices that still had > yet to be probed and not being able to use registration completion vs > the device_lock() to effectively synchronize the sub-system. Why do you need to "synchronize the sub-system"? The asynchronous probing should be transparent to the driver. Just unregister the device (or the driver) and driver core will ensure that probe() is not in flight. Confused. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
