-----Original Message----- From: Parav Pandit parav@nvidia.com Sent: Wednesday, October 7, 2020 9:56 PM To: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com; Ertman, David M david.m.ertman@intel.com; Leon Romanovsky leon@kernel.org Cc: alsa-devel@alsa-project.org; parav@mellanox.com; tiwai@suse.de; netdev@vger.kernel.org; ranjani.sridharan@linux.intel.com; fred.oh@linux.intel.com; linux-rdma@vger.kernel.org; dledford@redhat.com; broonie@kernel.org; Jason Gunthorpe jgg@nvidia.com; gregkh@linuxfoundation.org; kuba@kernel.org; Williams, Dan J dan.j.williams@intel.com; Saleem, Shiraz shiraz.saleem@intel.com; davem@davemloft.net; Patil, Kiran kiran.patil@intel.com Subject: RE: [PATCH v2 1/6] Add ancillary bus support
From: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com Sent: Thursday, October 8, 2020 3:20 AM
On 10/7/20 4:22 PM, Ertman, David M wrote:
-----Original Message----- From: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com Sent: Wednesday, October 7, 2020 1:59 PM To: Ertman, David M david.m.ertman@intel.com; Parav Pandit parav@nvidia.com; Leon Romanovsky leon@kernel.org Cc: alsa-devel@alsa-project.org; parav@mellanox.com; tiwai@suse.de; netdev@vger.kernel.org; ranjani.sridharan@linux.intel.com; fred.oh@linux.intel.com; linux-rdma@vger.kernel.org; dledford@redhat.com; broonie@kernel.org; Jason Gunthorpe jgg@nvidia.com; gregkh@linuxfoundation.org; kuba@kernel.org; Williams, Dan J dan.j.williams@intel.com; Saleem, Shiraz shiraz.saleem@intel.com; davem@davemloft.net; Patil, Kiran kiran.patil@intel.com Subject: Re: [PATCH v2 1/6] Add ancillary bus support
Below is most simple, intuitive and matching with core APIs for name and design pattern wise. init() { err = ancillary_device_initialize(); if (err) return ret;
err = ancillary_device_add(); if (ret) goto err_unwind;
err = some_foo(); if (err) goto err_foo; return 0;
err_foo: ancillary_device_del(adev); err_unwind: ancillary_device_put(adev->dev); return err; }
cleanup() { ancillary_device_de(adev); ancillary_device_put(adev); /* It is common to have a one wrapper for this as ancillary_device_unregister(). * This will match with core device_unregister() that has precise documentation. * but given fact that init() code need proper error unwinding, like above, * it make sense to have two APIs, and no need to export another symbol for unregister(). * This pattern is very easy to audit and code. */ }
I like this flow +1
But ... since the init() function is performing both device_init and device_add - it should probably be called ancillary_device_register, and we are back to a single exported API for both register and unregister.
Kind reminder that we introduced the two functions to allow the caller to know if it needed to free memory when initialize() fails, and it didn't need to free memory when add() failed since put_device() takes care of it. If you have a single init() function it's impossible to know which behavior to select on error.
I also have a case with SoundWire where it's nice to first initialize, then set some data and then add.
The flow as outlined by Parav above does an initialize as the first step, so every error path out of the function has to do a put_device(), so you would never need to manually free the memory in
the setup function.
It would be freed in the release call.
err = ancillary_device_initialize(); if (err) return ret;
where is the put_device() here? if the release function does any sort of kfree, then you'd need to do it manually in this case.
Since device_initialize() failed, put_device() cannot be done here. So yes, pseudo code should have shown, if (err) { kfree(adev); return err; }
If we just want to follow register(), unregister() pattern,
Than,
ancillar_device_register() should be,
/**
- ancillar_device_register() - register an ancillary device
- NOTE: __never directly free @adev after calling this function, even if it
returned
- an error. Always use ancillary_device_put() to give up the reference
initialized by this function.
- This note matches with the core and caller knows exactly what to be done.
*/ ancillary_device_register() { device_initialize(&adev->dev); if (!dev->parent || !adev->name) return -EINVAL; if (!dev->release && !(dev->type && dev->type->release)) { /* core is already capable and throws the warning when release callback is not set. * It is done at drivers/base/core.c:1798. * For NULL release it says, "does not have a release() function, it is broken and must be fixed" */ return -EINVAL; }
That code is in device_release(). Because of this check we will never hit that code.
We either need to leave the error message here, or if we are going to rely on the core to find this condition at the end of the process, then we need to completely remove this check from the registration flow.
-DaveE