On 03/12/2018 08:00 AM, Rasmus Villemoes wrote:
On 2018-03-10 01:10, Laura Abbott wrote:
                /* collect all inputs belonging to the same chip */
                first = i;
-               memset(mask, 0, sizeof(mask));
+               memset(mask, 0, sizeof(*mask));

see below

@@ -2887,14 +2909,30 @@ void gpiod_set_array_value_complex(bool raw, bool 
while (i < array_size) {
                struct gpio_chip *chip = desc_array[i]->gdev->chip;
-               unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
-               unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
+               unsigned long *mask;
+               unsigned long *bits;
                int count = 0;
+ mask = kmalloc_array(BITS_TO_LONGS(chip->ngpio),
+                               sizeof(*mask),
+                               can_sleep ? GFP_KERNEL : GFP_ATOMIC);
+               if (!mask)
+                       return;
+               bits = kmalloc_array(BITS_TO_LONGS(chip->ngpio),
+                               sizeof(*bits),
+                               can_sleep ? GFP_KERNEL : GFP_ATOMIC);
+               if (!bits) {
+                       kfree(mask);
+                       return;
+               }
                if (!can_sleep)
- memset(mask, 0, sizeof(mask));
+               memset(mask, 0, sizeof(*mask));

Hm, it seems you're now only clearing the first word of mask, not the
entire allocation. Why not just use kcalloc() instead of kmalloc_array
to have it automatically cleared?

Bleh, I didn't think through that carefully. I'll just switch
to kcalloc, especially since it calls kmalloc_array.

Other random thoughts: maybe two allocations for each loop iteration is
a bit much. Maybe do a first pass over the array and collect the maximal
chip->ngpio, do the memory allocation and freeing outside the loop (then
you'd of course need to preserve the memset() with appropriate length
computed). And maybe even just do one allocation, making bits point at
the second half.

I was trying to make minimal changes and match the existing code. Is this
likely to be an actual hot path to optimize?

Does the set function need to be updated to return an int to be able to
inform the caller that memory allocation failed?

That would involve changing the public API. I don't have a problem
doing so if that's what you want.



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