From: Alexander Duyck <firstname.lastname@example.org> To: Bart Van Assche <email@example.com>, Alexander Duyck <firstname.lastname@example.org> Cc: Greg KH <email@example.com>, LKML <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Tejun Heo <email@example.com>, Andrew Morton <firstname.lastname@example.org> Subject: Re: [driver-core PATCH v4 4/6] driver core: Probe devices asynchronously instead of the driver Date: Fri, 19 Oct 2018 15:35:06 -0700 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> On Thu, 2018-10-18 at 19:31 -0700, Bart Van Assche wrote: > On 10/18/18 7:20 PM, Alexander Duyck wrote: > > I see what you are talking about now. Actually I think this was an > > existing issue before my patch even came into play. Basically the > > code > > as it currently stands is device specific in terms of the attach > > and > > release code. > > > > I wonder if we shouldn't have the async_synchronize_full call in > > __device_release_driver moved down and into driver_detach before we > > even start the for loop. Assuming the driver is no longer > > associated > > with the bus that should flush out all devices so that we can then > > pull them out of the devices list at least. I may look at adding an > > additional bitflag to the device struct to indicate that it has a > > driver attach pending. Then for things like races between any > > attach > > and detach calls the logic becomes pretty straight forward. Attach > > will set the bit and provide driver data, detach will clear the bit > > and the driver data. If a driver loads in between it should clear > > the > > bit as well. > > > > I'll work on it over the next couple days and hopefully have > > something > > ready for testing/review early next week. > > Hi Alex, > > How about checking in __driver_attach_async_helper() whether the > driver > pointer is still valid by checking whether bus_for_each_drv(dev- > >bus, > ...) can still find the driver pointer? That approach requires > protection with a mutex to avoid races with the driver detach code > but > shouldn't require any new flags in struct device. > > Thanks, > > Bart. That doesn't solve the problem I was pointing out though. So the issue you are addressing by rechecking the bus should already be handled by just calling async_synchronize_full in driver_detach. After all we can't have a driver that is being added to the bus while it is also being removed. So if we are detaching the driver calling async_synchronize_full will flush out any deferred attach calls and there will be no further calls since the driver has already been removed from the bus. The issue I was thinking of is how do we deal with races between device_attach and device_release_driver. In that case we know the device we want to remove a driver from, but we may not have information about the driver. The easiest solution is to basically just disable the pending enable. I could use the approach I am doing now and just NULL out the driver_data if dev->driver is NULL. The only thing I am thinking about is if just dev->driver being NULL is enough to signal that we are using driver_data to carry a pointer to a pending driver, or if we should add an extra bit to carry that meaning. It would be pretty easy to just add a bit and then use that to prevent any false reads of the deferred driver as driver data, or driver data as a deferred driver as it would essentially act as a type bit. Thanks. - Alex
next prev parent reply other threads:[~2018-10-19 22:35 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-10-15 15:09 [driver-core PATCH v4 0/6] Add NUMA aware async_schedule calls Alexander Duyck 2018-10-15 15:09 ` [driver-core PATCH v4 1/6] workqueue: Provide queue_work_node to queue work near a given NUMA node Alexander Duyck 2018-10-15 15:09 ` [driver-core PATCH v4 2/6] async: Add support for queueing on specific " Alexander Duyck 2018-10-15 15:09 ` [driver-core PATCH v4 3/6] device core: Consolidate locking and unlocking of parent and device Alexander Duyck 2018-10-18 7:46 ` Rafael J. Wysocki 2018-10-18 17:53 ` Bart Van Assche 2018-10-15 15:09 ` [driver-core PATCH v4 4/6] driver core: Probe devices asynchronously instead of the driver Alexander Duyck 2018-10-18 18:11 ` Bart Van Assche 2018-10-18 19:38 ` Alexander Duyck 2018-10-18 20:13 ` Bart Van Assche 2018-10-19 2:20 ` Alexander Duyck 2018-10-19 2:31 ` Bart Van Assche 2018-10-19 22:35 ` Alexander Duyck [this message] 2018-10-15 15:09 ` [driver-core PATCH v4 5/6] driver core: Attach devices on CPU local to device node Alexander Duyck 2018-10-15 15:09 ` [driver-core PATCH v4 6/6] PM core: Use new async_schedule_dev command Alexander Duyck
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