Messages in this thread | | | Subject | Re: [PATCH 1/4] gpio: Remove VLA from gpiolib | From | Laura Abbott <> | Date | Mon, 12 Mar 2018 16:40:50 -0700 |
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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 can_sleep, >> >> 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) >> WARN_ON(chip->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.
> Rasmus >
Thanks, Laura
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