[Linaro-mm-sig] Re: [PATCH] dma-buf/fence-array: Add flex array to struct dma_fence_array

Am 18.05.24 um 19:47 schrieb Christophe JAILLET:

This is an effort to get rid of all multiplications from allocation functions in order to prevent integer overflows [1][2].

The "struct dma_fence_array" can be refactored to add a flex array in order to have the "callback structures allocated behind the array" be more explicit.

Do so: - makes the code more readable and safer. - allows using __counted_by() for additional checks - avoids some pointer arithmetic in dma_fence_array_enable_signaling()

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-ar... [1] Link: https://github.com/KSPP/linux/issues/160 [2] Signed-off-by: Christophe JAILLET christophe.jaillet@wanadoo.fr

---

Compile tested only.

Also, I don't think that 'cb' is a great name and the associated kernel-doc description could certainly be improved. Any proposal welcomed :)

Ah, yes. That was also on my TODO list for a very long time.

---

drivers/dma-buf/dma-fence-array.c | 10 ++++------ include/linux/dma-fence-array.h | 3 +++ 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 9b3ce8948351..9c55afaca607 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -70,7 +70,7 @@ static void dma_fence_array_cb_func(struct dma_fence *f, static bool dma_fence_array_enable_signaling(struct dma_fence *fence) { struct dma_fence_array *array = to_dma_fence_array(fence);

• struct dma_fence_array_cb *cb = (void *)(&array[1]);

• struct dma_fence_array_cb *cb = array->cb; unsigned i;

for (i = 0; i < array->num_fences; ++i) { @@ -168,22 +168,20 @@ struct dma_fence_array *dma_fence_array_create(int num_fences, bool signal_on_any) { struct dma_fence_array *array;

• size_t size = sizeof(*array);

WARN_ON(!num_fences || !fences);

• /* Allocate the callback structures behind the array. */
• size += num_fences * sizeof(struct dma_fence_array_cb);
• array = kzalloc(size, GFP_KERNEL);

• array = kzalloc(struct_size(array, cb, num_fences), GFP_KERNEL); if (!array) return NULL;

• array->num_fences = num_fences;
• spin_lock_init(&array->lock); dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock, context, seqno); init_irq_work(&array->work, irq_dma_fence_array_work);

• array->num_fences = num_fences; atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences); array->fences = fences;

diff --git a/include/linux/dma-fence-array.h b/include/linux/dma-fence-array.h index ec7f25def392..a793f9d5c73b 100644 --- a/include/linux/dma-fence-array.h +++ b/include/linux/dma-fence-array.h @@ -33,6 +33,7 @@ struct dma_fence_array_cb {

• @num_pending: fences in the array still pending
• @fences: array of the fences
• @work: internal irq_work function

• • @cb: array of callback helpers
  */ struct dma_fence_array { struct dma_fence base;

@@ -43,6 +44,8 @@ struct dma_fence_array { struct dma_fence **fences; struct irq_work work;

• struct dma_fence_array_cb cb[] __counted_by(num_fences);

Please name that callbacks, apart from that looks good to me.

Regards, Christian.

}; /**