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

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check
Date	2017-01-16 11:00 +0100
Message-ID	<t0ceZ-71a-3@gated-at.bofh.it> (permalink)
References	<t0bCi-6HI-19@gated-at.bofh.it> <t0bLY-6Q2-9@gated-at.bofh.it> <t0bVE-6TE-27@gated-at.bofh.it> <t0c5j-6Xo-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Mon 16-01-17 11:48:51, Leon Romanovsky wrote:
> 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@suse.de>
> > > >
> > > > We wanna know who's doing such a thing. Like slab.c does that.
> > > >
> > > > Signed-off-by: Borislav Petkov <bp@suse.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.

On the other hand WARN* will taint the kernel and this sounds a bit
overreacting for something like a wrong gfp mask which is perfectly
recoverable. Not to mention users who care configured to panic on
warning.

So while I do not have a strong opinion on this I would rather stay with
the dump_stack.


-- 
Michal Hocko
SUSE Labs

Thread

[PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Borislav Petkov <bp@alien8.de> - 2017-01-16 10:20 +0100
  Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Leon Romanovsky <leon@kernel.org> - 2017-01-16 10:30 +0100
    Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Borislav Petkov <bp@alien8.de> - 2017-01-16 10:40 +0100
      Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Leon Romanovsky <leon@kernel.org> - 2017-01-16 10:50 +0100
        Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Michal Hocko <mhocko@kernel.org> - 2017-01-16 11:00 +0100
        Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Borislav Petkov <bp@alien8.de> - 2017-01-16 11:00 +0100
          Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Leon Romanovsky <leon@kernel.org> - 2017-01-16 11:20 +0100
            Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Leon Romanovsky <leon@kernel.org> - 2017-01-16 11:20 +0100
            Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Borislav Petkov <bp@alien8.de> - 2017-01-16 11:20 +0100
  Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Michal Hocko <mhocko@kernel.org> - 2017-01-16 10:40 +0100
  Re: [PATCH] mm/slub: Add a dump_stack() to the unexpected GFP check Vlastimil Babka <vbabka@suse.cz> - 2017-01-16 11:10 +0100

csiph-web