linux-kernel - Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check

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Date:   Mon, 16 Jan 2017 11:48:51 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michal Hocko <mhocko@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check

On Mon, Jan 16, 2017 at 10:37:02AM +0100, Borislav Petkov wrote:
> On Mon, Jan 16, 2017 at 11:28:40AM +0200, Leon Romanovsky wrote:
> > On Mon, Jan 16, 2017 at 10:16:43AM +0100, Borislav Petkov wrote:
> > > From: Borislav Petkov <bp@...e.de>
> > >
> > > We wanna know who's doing such a thing. Like slab.c does that.
> > >
> > > Signed-off-by: Borislav Petkov <bp@...e.de>
> > > ---
> > >  mm/slub.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 067598a00849..1b0fa7625d6d 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -1623,6 +1623,7 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
> > >  		flags &= ~GFP_SLAB_BUG_MASK;
> > >  		pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n",
> > >  				invalid_mask, &invalid_mask, flags, &flags);
> > > +		dump_stack();
> >
> > Will it make sense to change these two lines above to WARN(true, .....)?
>
> Should be equivalent.

Almost, except one point - pr_warn and dump_stack have different log
levels. There is a chance that user won't see pr_warn message above, but
dump_stack will be always present.

For WARN_XXX, users will always see message and stack at the same time.

>
> I'd even go a step further and make this a small inline function,
> something like warn_unexpected_gfp(flags) or so and call it from both
> from slab.c and slub.c.
>
> Depending on what mm folks prefer, that is.
>
> --
> Regards/Gruss,
>     Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.

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