Re: [PATCH 7/9] mm, slub: introduce kmem_cache_debug_flags()

From: Roman Gushchin <guro@fb.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>, <kernel-team@android.com>,
	<vinmenon@codeaurora.org>, Kees Cook <keescook@chromium.org>,
	Matthew Garrett <mjg59@google.com>, Jann Horn <jannh@google.com>,
	Vijayanand Jitta <vjitta@codeaurora.org>
Subject: Re: [PATCH 7/9] mm, slub: introduce kmem_cache_debug_flags()
Date: Wed, 10 Jun 2020 15:06:12 -0700	[thread overview]
Message-ID: <20200610220612.GB702969@carbon.DHCP.thefacebook.com> (raw)
In-Reply-To: <20200610163135.17364-8-vbabka@suse.cz>

On Wed, Jun 10, 2020 at 06:31:33PM +0200, Vlastimil Babka wrote:
> There are few places that call kmem_cache_debug(s) (which tests if any of debug
> flags are enabled for a cache) immediatelly followed by a test for a specific
> flag. The compiler can probably eliminate the extra check, but we can make the
> code nicer by introducing kmem_cache_debug_flags() that works like
> kmem_cache_debug() (including the static key check) but tests for specifig
> flag(s). The next patches will add more users.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/slub.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)

Acked-by: Roman Gushchin <guro@fb.com>

One small nit below.

> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 24d3e5f832aa..c8e8b4ae2451 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -122,18 +122,28 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);
>  #endif
>  #endif
>  
> -static inline int kmem_cache_debug(struct kmem_cache *s)
> +/*
> + * Returns true if any of the specified slub_debug flags is enabled for the
> + * cache. Use only for flags parsed by setup_slub_debug() as it also enables
> + * the static key.

Maybe adding VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)) to make sure the flags
argument is valid?

> + */
> +static inline int kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags)
>  {
>  #ifdef CONFIG_SLUB_DEBUG
>  	if (static_branch_unlikely(&slub_debug_enabled))
> -		return s->flags & SLAB_DEBUG_FLAGS;
> +		return s->flags & flags;
>  #endif
>  	return 0;
>  }
>  
> +static inline int kmem_cache_debug(struct kmem_cache *s)
> +{
> +	return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS);
> +}
> +
>  void *fixup_red_left(struct kmem_cache *s, void *p)
>  {
> -	if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE)
> +	if (kmem_cache_debug_flags(s, SLAB_RED_ZONE))
>  		p += s->red_left_pad;
>  
>  	return p;
> @@ -4076,7 +4086,7 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
>  	offset = (ptr - page_address(page)) % s->size;
>  
>  	/* Adjust for redzone and reject if within the redzone. */
> -	if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) {
> +	if (kmem_cache_debug_flags(s, SLAB_RED_ZONE)) {
>  		if (offset < s->red_left_pad)
>  			usercopy_abort("SLUB object in left red zone",
>  				       s->name, to_user, offset, n);
> -- 
> 2.26.2
> 