linux-kernel - Re: [PATCH] s390/pci: Remove unnecessary if condition

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Message-ID: <alpine.DEB.2.10.1608010838030.3078@hadrien>
Date:	Mon, 1 Aug 2016 08:39:32 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
cc:	Julia Lawall <julia.lawall@...6.fr>,
	Amitoj Kaur Chawla <amitoj1606@...il.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/pci: Remove unnecessary if condition



On Fri, 29 Jul 2016, Sebastian Ott wrote:

> On Fri, 29 Jul 2016, Julia Lawall wrote:
> > On Fri, 29 Jul 2016, Sebastian Ott wrote:
> > > On Fri, 29 Jul 2016, Amitoj Kaur Chawla wrote:
> > > > Remove unnecessary error handling because the only failure value that
> > > > can be returned is NULL and so the test can never be true.
> > > >
> > > > The Coccinelle semantic patch used to make this change is as follows:
> > > > @@
> > > > expression e;
> > > > @@
> > > >
> > > >   e = debugfs_create_file(...);
> > > > - if(IS_ERR(e)) { e = NULL; }
> > >
> > > Nope. For !CONFIG_DEBUG_FS debugfs_create_file returns an ERR_PTR.
> >
> > Clicking around in lxr doesn't show that, but perhaps an alternative
> > definition is overlooked?
>
> It looks that way.
>
>
> [sebott@...leppi linux]$ git grep -W "debugfs_create_file(" include/linux/debugfs.h
> include/linux/debugfs.h:struct dentry *debugfs_create_file(const char *name, umode_t mode,
> include/linux/debugfs.h-                                   struct dentry *parent, void *data,
> include/linux/debugfs.h-                                   const struct file_operations *fops);
> --
> include/linux/debugfs.h:static inline struct dentry *debugfs_create_file(const char *name, umode_t mode,
> include/linux/debugfs.h-                                        struct dentry *parent, void *data,
> include/linux/debugfs.h-                                        const struct file_operations *fops)
> include/linux/debugfs.h-{
> include/linux/debugfs.h-        return ERR_PTR(-ENODEV);
> include/linux/debugfs.h-}
> include/linux/debugfs.h-

Thanks for the pointer.  I guess that if the result of debugfs_create_file
is actully dereferenced, then both test should be present, eg:

drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c

       ent = debugfs_create_file(name,
                                 S_IFREG | S_IRUGO, root,
                                 ring, &amdgpu_debugfs_ring_fops);
       if (IS_ERR(ent))
		return PTR_ERR(ent);

       i_size_write(ent->d_inode, ring->ring_size + 12);

This problem seems to only occur in this directory.

thanks,
julia