Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask

[Chunyu Hu <chuhu@redhat.com>]

----- Original Message -----
> From: "Catalin Marinas" <catalin.marinas@arm.com>
> To: "Michal Hocko" <mhocko@kernel.org>
> Cc: "Chunyu Hu" <chuhu.ncepu@gmail.com>, "Dmitry Vyukov" <dvyukov@google.com>, "Chunyu Hu" <chuhu@redhat.com>, "LKML"
> <linux-kernel@vger.kernel.org>, "Linux-MM" <linux-mm@kvack.org>
> Sent: Tuesday, April 24, 2018 9:41:48 PM
> Subject: Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask
> 
> On Tue, Apr 24, 2018 at 07:20:57AM -0600, Michal Hocko wrote:
> > On Mon 23-04-18 12:17:32, Chunyu Hu wrote:
> > [...]
> > > So if there is a new flag, it would be the 25th bits.
> > 
> > No new flags please. Can you simply store a simple bool into
> > fail_page_alloc
> > and have save/restore api for that?
> 
> For kmemleak, we probably first hit failslab. Something like below may
> do the trick:
> 
> diff --git a/mm/failslab.c b/mm/failslab.c
> index 1f2f248e3601..63f13da5cb47 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -29,6 +29,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t
> gfpflags)
>  	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
>  		return false;
>  
> +	if (s->flags & SLAB_NOLEAKTRACE)
> +		return false;
> +
>  	return should_fail(&failslab.attr, s->object_size);
>  }

This maybe is the easy enough way for skipping fault injection for kmemleak slab object. 
 
>  
> 
> Can we get a second should_fail() via should_fail_alloc_page() if a new
> slab page is allocated?

looking at code path blow, what do you mean by getting a second should_fail() via
fail_alloc_page?  Seems we need to insert the flag between alloc_slab_page and 
alloc_pages()? Without GFP flag, it's difficult to pass info to should_fail_alloc_page
and keep simple at same time. 

Or as Michal suggested, completely disabling page alloc fail injection when kmemleak
enabled. And enable it again when kmemleak off. 

 alloc_slab_page   
          <========= flag to change the behavior of should_fail_alloc_page
     alloc_pages
         alloc_pages_current
             __alloc_pages_nodemask
                 prepare_alloc_pages
                     should_fail_alloc_page

> 
> --
> Catalin
> 

-- 
Regards,
Chunyu Hu