linux-kernel - Re: [PATCH] fail_function: no need to check return value of debugfs

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Date:   Wed, 23 Jan 2019 07:33:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Josef Bacik <jbacik@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        zhong jiang <zhongjiang@...wei.com>
Subject: Re: [PATCH] fail_function: no need to check return value of
 debugfs_create functions

On Wed, Jan 23, 2019 at 09:11:41AM +0900, Masami Hiramatsu wrote:
> On Tue, 22 Jan 2019 16:21:44 +0100
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> 
> > 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.
> 
> Ah, OK. It simplifies the code. But I have a question below,
> 
> > 
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Josef Bacik <jbacik@...com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
> > Cc: zhong jiang <zhongjiang@...wei.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> >  kernel/fail_function.c | 23 +++++------------------
> >  1 file changed, 5 insertions(+), 18 deletions(-)
> > 
> > diff --git a/kernel/fail_function.c b/kernel/fail_function.c
> > index 17f75b545f66..afc779be5ebb 100644
> > --- a/kernel/fail_function.c
> > +++ b/kernel/fail_function.c
> > @@ -152,20 +152,13 @@ static int fei_retval_get(void *data, u64 *val)
> >  DEFINE_DEBUGFS_ATTRIBUTE(fei_retval_ops, fei_retval_get, fei_retval_set,
> >  			 "%llx\n");
> >  
> > -static int fei_debugfs_add_attr(struct fei_attr *attr)
> > +static void fei_debugfs_add_attr(struct fei_attr *attr)
> >  {
> >  	struct dentry *dir;
> >  
> >  	dir = debugfs_create_dir(attr->kp.symbol_name, fei_debugfs_dir);
> > -	if (!dir)
> > -		return -ENOMEM;
> > -
> > -	if (!debugfs_create_file("retval", 0600, dir, attr, &fei_retval_ops)) {
> > -		debugfs_remove_recursive(dir);
> > -		return -ENOMEM;
> > -	}
> >  
> > -	return 0;
> 
> Don't we need to check dir here? If above debugfs_create_dir() returns NULL,
> it seems we will create "retval" under root directory of debugfs.

If NULL is returned, your system is out of memory and worse things are
about to happen :)

thanks,

greg k-h