linux-kernel - Re: [PATCH] zswap: ignore debugfs_create

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Date:   Tue, 29 Jan 2019 21:33:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Seth Jennings <sjenning@...hat.com>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH] zswap: ignore debugfs_create_dir() return value

On Tue, Jan 29, 2019 at 02:46:30PM -0500, Dan Streetman wrote:
> On Tue, Jan 22, 2019 at 10:23 AM 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.
> >
> > Cc: Seth Jennings <sjenning@...hat.com>
> > Cc: Dan Streetman <ddstreet@...e.org>
> > Cc: linux-mm@...ck.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> >  mm/zswap.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index a4e4d36ec085..f583d08f6e24 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -1262,8 +1262,6 @@ static int __init zswap_debugfs_init(void)
> >                 return -ENODEV;
> >
> >         zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
> > -       if (!zswap_debugfs_root)
> > -               return -ENOMEM;
> >
> >         debugfs_create_u64("pool_limit_hit", 0444,
> >                            zswap_debugfs_root, &zswap_pool_limit_hit);
> 
> wait, so if i'm reading the code right, in the case where
> debugfs_create_dir() returns NULL, that will then be passed along to
> debugfs_create_u64() as its parent directory - and the debugfs nodes
> will then get created in the root debugfs directory.  That's not what
> we want to happen...

True, but that is such a rare thing to ever happen (hint, you have to be
out of memory), that it's not really a bad thing.  But, you are not the
first to mention this, which is why this patch is on its way to Linus
for 5.0-final:
	https://lore.kernel.org/lkml/20190123102814.GB17123@kroah.com/

thanks,

greg k-h