linux-kernel - Re: [PATCH 1/2] drm: replace drm_[cm]alloc* by kvmalloc alternatives

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Date:   Wed, 17 May 2017 11:03:50 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH 1/2] drm: replace drm_[cm]alloc* by kvmalloc alternatives

On Wed 17-05-17 08:38:09, Chris Wilson wrote:
> On Wed, May 17, 2017 at 08:55:08AM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > drm_[cm]alloc* has grown their own kvmalloc with vmalloc fallback
> > implementations. MM has grown kvmalloc* helpers in the meantime. Let's
> > use those because it a) reduces the code and b) MM has a better idea
> > how to implement fallbacks (e.g. do not vmalloc before kmalloc is tried
> > with __GFP_NORETRY).
> > 
> > drm_calloc_large needs to get __GFP_ZERO explicitly but it is the same
> > thing as kvmalloc_array in principle.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> 
> Just a little surprised that calloc_large users still exist.
> 
> Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>

Thanks!

> One more feature request from mm, can we have the 
> 	if (size != 0 && n > SIZE_MAX / size)
> check exported by itself.

What do you exactly mean by exporting? Something like the following?
I haven't compile tested it outside of mm with different config options.
Sticking alloc_array_check into mm_types.h is kind of gross but I do not
have a great idea where to put it. A new header doesn't seem nice.
---
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7cb17c6b97de..f908b14ffc4c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -534,7 +534,7 @@ static inline void *kvzalloc(size_t size, gfp_t flags)
 
 static inline void *kvmalloc_array(size_t n, size_t size, gfp_t flags)
 {
-	if (size != 0 && n > SIZE_MAX / size)
+	if (!alloc_array_check(n, size))
 		return NULL;
 
 	return kvmalloc(n * size, flags);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 45cdb27791a3..d7154b43a0d1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -601,4 +601,10 @@ typedef struct {
 	unsigned long val;
 } swp_entry_t;
 
+static inline bool alloc_array_check(size_t n, size_t size)
+{
+	if (size != 0 && n > SIZE_MAX / size)
+		return false;
+	return true;
+}
 #endif /* _LINUX_MM_TYPES_H */
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 3c37a8c51921..e936ca7c55a1 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -602,7 +602,7 @@ int memcg_update_all_caches(int num_memcgs);
  */
 static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
 {
-	if (size != 0 && n > SIZE_MAX / size)
+	if (!alloc_array_check(n, size))
 		return NULL;
 	if (__builtin_constant_p(n) && __builtin_constant_p(size))
 		return kmalloc(n * size, flags);

-- 
Michal Hocko
SUSE Labs