netdev - Re: [PATCH 2/8] fwctl: Basic ioctl dispatch for the character device

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Date: Tue, 4 Jun 2024 15:22:21 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Zhu Yanjun <zyjzyj2000@...il.com>
Cc: Jason Gunthorpe <jgg@...dia.com>, Jonathan Corbet <corbet@....net>,
	Itay Avraham <itayavr@...dia.com>, Jakub Kicinski <kuba@...nel.org>,
	linux-doc@...r.kernel.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
	Saeed Mahameed <saeedm@...dia.com>,
	Tariq Toukan <tariqt@...dia.com>,
	Andy Gospodarek <andrew.gospodarek@...adcom.com>,
	Aron Silverton <aron.silverton@...cle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Ahern <dsahern@...nel.org>,
	Christoph Hellwig <hch@...radead.org>, Jiri Pirko <jiri@...dia.com>,
	Leonid Bloch <lbloch@...dia.com>, linux-cxl@...r.kernel.org,
	patches@...ts.linux.dev
Subject: Re: [PATCH 2/8] fwctl: Basic ioctl dispatch for the character device

On Tue, Jun 04, 2024 at 02:16:12PM +0200, Zhu Yanjun wrote:
> On 03.06.24 17:53, Jason Gunthorpe wrote:
> > Each file descriptor gets a chunk of per-FD driver specific context that
> > allows the driver to attach a device specific struct to. The core code
> > takes care of the memory lifetime for this structure.
> > 
> > The ioctl dispatch and design is based on what was built for iommufd. The
> > ioctls have a struct which has a combined in/out behavior with a typical
> > 'zero pad' scheme for future extension and backwards compatibility.
> > 
> > Like iommufd some shared logic does most of the ioctl marshalling and
> > compatibility work and tables diatches to some function pointers for
> > each unique iotcl.
> > 
> > This approach has proven to work quite well in the iommufd and rdma
> > subsystems.
> > 
> > Allocate an ioctl number space for the subsystem.
> > 
> > Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> > ---
> >   .../userspace-api/ioctl/ioctl-number.rst      |   1 +
> >   MAINTAINERS                                   |   1 +
> >   drivers/fwctl/main.c                          | 124 +++++++++++++++++-
> >   include/linux/fwctl.h                         |  31 +++++
> >   include/uapi/fwctl/fwctl.h                    |  41 ++++++
> >   5 files changed, 196 insertions(+), 2 deletions(-)
> >   create mode 100644 include/uapi/fwctl/fwctl.h

<...>

> >   static int fwctl_fops_open(struct inode *inode, struct file *filp)
> >   {
> >   	struct fwctl_device *fwctl =
> >   		container_of(inode->i_cdev, struct fwctl_device, cdev);
> > +	struct fwctl_uctx *uctx __free(kfree) = NULL;
> > +	int ret;
> > +
> > +	guard(rwsem_read)(&fwctl->registration_lock);
> > +	if (!fwctl->ops)
> > +		return -ENODEV;
> > +
> > +	uctx = kzalloc(fwctl->ops->uctx_size, GFP_KERNEL |  GFP_KERNEL_ACCOUNT);
> > +	if (!uctx)
> > +		return -ENOMEM;
> > +
> > +	uctx->fwctl = fwctl;
> > +	ret = fwctl->ops->open_uctx(uctx);
> > +	if (ret)
> > +		return ret;
> 
> When something is wrong, uctx is freed in "fwctl->ops->open_uctx(uctx);"?
> 
> If not, the allocated memory uctx leaks here.

See how uctx is declared:
struct fwctl_uctx *uctx __free(kfree) = NULL;

It will be released automatically.
See include/linux/cleanup.h for more details.

Thanks