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

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Message-ID: <CALZtONBSgcHMLZBAdc3FmGFbVrQhvdWKpKe+ATSuGk8_D=QP_A@mail.gmail.com>
Date:   Thu, 31 Jan 2019 11:09:09 -0500
From:   Dan Streetman <ddstreet@...e.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.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 3:33 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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/

Ah!  Great, in that case then definitely

Acked-by: Dan Streetman <ddstreet@...e.org>

>
> thanks,
>
> greg k-h