Messages in this thread | | | Subject | Re: [driver-core PATCH v8 2/9] driver core: Establish order of operations for device_add and device_del via bitflag | From | Alexander Duyck <> | Date | Mon, 10 Dec 2018 12:57:44 -0800 |
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On Mon, 2018-12-10 at 11:43 -0800, Dan Williams wrote: > On Mon, Dec 10, 2018 at 11:35 AM Alexander Duyck > <alexander.h.duyck@linux.intel.com> wrote: > > > > On Mon, 2018-12-10 at 10:58 -0800, Dan Williams wrote: > > > On Wed, Dec 5, 2018 at 9:25 AM Alexander Duyck > > > <alexander.h.duyck@linux.intel.com> wrote: > > > > > > > > Add an additional bit flag to the device struct named "dead". > > > > > > > > This additional flag provides a guarantee that when a device_del is > > > > executed on a given interface an async worker will not attempt to attach > > > > the driver following the earlier device_del call. Previously this > > > > guarantee was not present and could result in the device_del call > > > > attempting to remove a driver from an interface only to have the async > > > > worker attempt to probe the driver later when it finally completes the > > > > asynchronous probe call. > > > > > > > > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > > > --- > > > > drivers/base/core.c | 11 +++++++++++ > > > > drivers/base/dd.c | 8 ++++++-- > > > > include/linux/device.h | 5 +++++ > > > > 3 files changed, 22 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c > > > > index f3e6ca4170b4..70358327303b 100644 > > > > --- a/drivers/base/core.c > > > > +++ b/drivers/base/core.c > > > > @@ -2075,6 +2075,17 @@ void device_del(struct device *dev) > > > > struct kobject *glue_dir = NULL; > > > > struct class_interface *class_intf; > > > > > > > > + /* > > > > + * Hold the device lock and set the "dead" flag to guarantee that > > > > + * the update behavior is consistent with the other bitfields near > > > > + * it and that we cannot have an asynchronous probe routine trying > > > > + * to run while we are tearing out the bus/class/sysfs from > > > > + * underneath the device. > > > > + */ > > > > + device_lock(dev); > > > > + dev->dead = true; > > > > + device_unlock(dev); > > > > + > > > > /* Notify clients of device removal. This call must come > > > > * before dpm_sysfs_remove(). > > > > */ > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > > > > index 88713f182086..3bb8c3e0f3da 100644 > > > > --- a/drivers/base/dd.c > > > > +++ b/drivers/base/dd.c > > > > @@ -774,6 +774,10 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie) > > > > > > > > device_lock(dev); > > > > > > > > + /* device is or has been removed from the bus, just bail out */ > > > > + if (dev->dead) > > > > + goto out_unlock; > > > > + > > > > > > What do you think about moving this check into > > > __device_attach_driver() alongside all the other checks? That way we > > > also get ->dead checking through the __device_attach() path. > > > > I'm not really sure that is the best spot to do that. Part of the > > reason being that by placing it where I did we avoid messing with the > > runtime power management for the parent if it was already powered off. > > ...but this already a rare event and the parent shouldn't otherwise be > bothered by a spurious pm_runtime wakeup event. > > > If anything I would say we could probably look at pulling the check out > > and placing the driver check in __device_attach_async_helper since from > > what I can tell the check is actually redundant in the non-async path > > anyway since __device_attach already had taken the device lock and > > checked dev->driver prior to calling __device_attach_driver. > > > > > ...and after that maybe it could be made a common helper > > > (dev_driver_checks()?) shared between __device_attach_driver() and > > > __driver_attach() to reduce some duplication. > > > > I'm not sure consolidating it into a function would really be worth the > > extra effort. It would essentially just obfuscate the checks and I am > > not sure you really save much with: > > if (dev_driver_checks(dev)) > > vs: > > if (!dev->dead && !dev->driver) > > > > By the time you create the function and replace the few spots that are > > making these checks you would end up most likely adding more complexity > > to the kernel rather than reducing it any. > > No, I was talking about removing this duplication in > __device_attach_driver() and __driver_attach(): > > if (ret == 0) { > /* no match */ > return 0; > } else if (ret == -EPROBE_DEFER) { > dev_dbg(dev, "Device match requests probe deferral\n"); > driver_deferred_probe_add(dev);
Is this bit of code correct? Seems like there should be a return here doesn't it?
I just double checked and this is what is in the kernel too.
> } else if (ret < 0) { > dev_dbg(dev, "Bus failed to match device: %d", ret); > return ret; > } /* ret > 0 means positive match */ > > ...and lead in with a dev->dead check.
I would think that we would want to check for dev->dead before we even call driver_match_device. That way we don't have the match function crawling around a device that is being disassembled. Is that what you were referring to?
Also the context for the two functions seems to be a bit different. In the case of __device_attach_driver the device_lock is already held. In __driver_attach the lock on the device isn't taken until after a match has been found.
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