linux-kernel - Re: [PATCH] mm/cma_debug: Check for null tmp in cma_debugfs_add

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Date:   Thu, 21 Feb 2019 09:36:24 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yue Hu <zbestahu@...il.com>, akpm@...ux-foundation.org,
        rientjes@...gle.com, joe@...ches.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, huyue2@...ong.com
Subject: Re: [PATCH] mm/cma_debug: Check for null tmp in cma_debugfs_add_one()

On Thu, Feb 21, 2019 at 09:23:09AM +0100, Michal Hocko wrote:
> On Thu 21-02-19 12:01:30, Yue Hu wrote:
> > From: Yue Hu <huyue2@...ong.com>
> > 
> > If debugfs_create_dir() failed, the following debugfs_create_file()
> > will be meanless since it depends on non-NULL tmp dentry and it will
> > only waste CPU resource.
> 
> The file will be created in the debugfs root. But, more importantly.
> Greg (CCed now) is working on removing the failure paths because he
> believes they do not really matter for debugfs and they make code more
> ugly. More importantly a check for NULL is not correct because you
> get ERR_PTR after recent changes IIRC.
> 
> > 
> > Signed-off-by: Yue Hu <huyue2@...ong.com>
> > ---
> >  mm/cma_debug.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/mm/cma_debug.c b/mm/cma_debug.c
> > index 2c2c869..3e9d984 100644
> > --- a/mm/cma_debug.c
> > +++ b/mm/cma_debug.c
> > @@ -169,6 +169,8 @@ static void cma_debugfs_add_one(struct cma *cma, struct dentry *root_dentry)
> >  	scnprintf(name, sizeof(name), "cma-%s", cma->name);
> >  
> >  	tmp = debugfs_create_dir(name, root_dentry);
> > +	if (!tmp)
> > +		return;

Ick, yes, this patch isn't ok, I've been doing lots of work to rip these
checks out :)

Thanks for catching this Michal.

greg k-h