drm/i915: Add flex arrays to struct i915_syncmap

The "struct i915_syncmap" uses a dynamically sized set of trailing
elements. It can use an "u32" array or a "struct i915_syncmap *"
array.

So, use the preferred way in the kernel declaring flexible arrays [1].
Because there are two possibilities for the trailing arrays, it is
necessary to declare a union and use the DECLARE_FLEX_ARRAY macro.

The comment can be removed as the union is now clear enough.

Also, avoid the open-coded arithmetic in the memory allocator functions
[2] using the "struct_size" macro.

Moreover, refactor the "__sync_seqno" and "__sync_child" functions due
to now it is possible to use the union members added to the structure.
This way, it is also possible to avoid the open-coded arithmetic in
pointers.

Link: https://www.kernel.org/doc/html/next/process/deprecated.html#zero-length-and-one-element-arrays
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
Signed-off-by: Erick Archer <erick.archer@gmx.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240208181318.4259-1-erick.archer@gmx.com

diff --git a/drivers/gpu/drm/i915/i915_syncmap.c b/drivers/gpu/drm/i915/i915_syncmap.c
index 60404dbb2e9fa9f3484989cdfe34bacd202d0ca9..df6437c37373df20f6a93b71887eb82a015757bd 100644 (file)
--- a/drivers/gpu/drm/i915/i915_syncmap.c
+++ b/drivers/gpu/drm/i915/i915_syncmap.c
@@ -75,13 +75,10 @@ struct i915_syncmap {
        unsigned int height;
        unsigned int bitmap;
        struct i915_syncmap *parent;
-       /*
-        * Following this header is an array of either seqno or child pointers:
-        * union {
-        *      u32 seqno[KSYNCMAP];
-        *      struct i915_syncmap *child[KSYNCMAP];
-        * };
-        */
+       union {
+               DECLARE_FLEX_ARRAY(u32, seqno);
+               DECLARE_FLEX_ARRAY(struct i915_syncmap *, child);
+       };
 };
 
 /**
@@ -99,13 +96,13 @@ void i915_syncmap_init(struct i915_syncmap **root)
 static inline u32 *__sync_seqno(struct i915_syncmap *p)
 {
        GEM_BUG_ON(p->height);
-       return (u32 *)(p + 1);
+       return p->seqno;
 }
 
 static inline struct i915_syncmap **__sync_child(struct i915_syncmap *p)
 {
        GEM_BUG_ON(!p->height);
-       return (struct i915_syncmap **)(p + 1);
+       return p->child;
 }
 
 static inline unsigned int
@@ -200,7 +197,7 @@ __sync_alloc_leaf(struct i915_syncmap *parent, u64 id)
 {
        struct i915_syncmap *p;
 
-       p = kmalloc(sizeof(*p) + KSYNCMAP * sizeof(u32), GFP_KERNEL);
+       p = kmalloc(struct_size(p, seqno, KSYNCMAP), GFP_KERNEL);
        if (unlikely(!p))
                return NULL;
 
@@ -282,7 +279,7 @@ static noinline int __sync_set(struct i915_syncmap **root, u64 id, u32 seqno)
                        unsigned int above;
 
                        /* Insert a join above the current layer */
-                       next = kzalloc(sizeof(*next) + KSYNCMAP * sizeof(next),
+                       next = kzalloc(struct_size(next, child, KSYNCMAP),
                                       GFP_KERNEL);
                        if (unlikely(!next))
                                return -ENOMEM;