Re: [PATCH 4/6] dma: pxa_dma: no need to check return value of debugfs_create functions

Greg Kroah-Hartman
2019-08-11T07:04:01Z

On Sat, Aug 10, 2019 at 09:27:26PM +0200, Robert Jarzmik wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
>
> Hi Greg,
>
> > When calling debugfs functions, there is no need to ever check the
> > return value. The function can work or not, but the code logic should
> > never do something different based on this.
> >
> > Also, because there is no need to save the file dentry, remove the
> > variable that was saving it as it was never even being used once set.
> >
> > Cc: Daniel Mack <daniel@zonque.org>
> > Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
> > Cc: Robert Jarzmik <robert.jarzmik@free.fr>
> > Cc: Vinod Koul <vkoul@kernel.org>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: dmaengine@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > drivers/dma/pxa_dma.c | 56 +++++++++----------------------------------
> > 1 file changed, 11 insertions(+), 45 deletions(-)
> >
> > diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
> > index b429642f3e7a..0f698f49ee26 100644
> > --- a/drivers/dma/pxa_dma.c
> > +++ b/drivers/dma/pxa_dma.c
> > @@ -132,7 +132,6 @@ struct pxad_device {
> > spinlock_t phy_lock; /* Phy association */
> > #ifdef CONFIG_DEBUG_FS
> > struct dentry *dbgfs_root;
> > - struct dentry *dbgfs_state;
> > struct dentry **dbgfs_chan;
> > #endif
> > };
> > @@ -326,31 +325,18 @@ static struct dentry *pxad_dbg_alloc_chan(struct pxad_device *pdev,
> > int ch, struct dentry *chandir)
> > {
> > char chan_name[11];
> > - struct dentry *chan, *chan_state = NULL, *chan_descr = NULL;
> > - struct dentry *chan_reqs = NULL;
> > + struct dentry *chan;
> > void *dt;
> >
> > scnprintf(chan_name, sizeof(chan_name), "%d", ch);
> > chan = debugfs_create_dir(chan_name, chandir);
> > dt = (void *)&pdev->phys[ch];
> >
> > - if (chan)
> > - chan_state = debugfs_create_file("state", 0400, chan, dt,
> > - &chan_state_fops);
> > - if (chan_state)
> > - chan_descr = debugfs_create_file("descriptors", 0400, chan, dt,
> > - &descriptors_fops);
> > - if (chan_descr)
> > - chan_reqs = debugfs_create_file("requesters", 0400, chan, dt,
> > - &requester_chan_fops);
> > - if (!chan_reqs)
> > - goto err_state;
> > + debugfs_create_file("state", 0400, chan, dt, &chan_state_fops);
> > + debugfs_create_file("descriptors", 0400, chan, dt, &descriptors_fops);
> > + debugfs_create_file("requesters", 0400, chan, dt, &requester_chan_fops);
>
> This is not strictly equivalent.
> Imagine that the debugfs_create_dir() fails and returns NULL :

How can that happen?

> - in the former case, neither "state", "descriptors" nor "requesters" would be
> created
> - in the new code, "state", "descriptors" nor "requesters" will be created in
> the debugfs root directory

I agree, but debugfs_create_dir() does not return a NULL on an error
since many kernel releases. Neither can debugfs_create_file() so really
this test is not working at all as-is :)

thanks,

greg k-h