Hi Yuanhan,
On Tue, Jan 08, 2013 at 10:57:53PM +0800, Yuanhan Liu wrote:
> The current kfifo API take the kfifo size as input, while it rounds
> _down_ the size to power of 2 at __kfifo_alloc. This may introduce
> potential issue.
>
> Take the code at drivers/hid/hid-logitech-dj.c as example:
>
> if (kfifo_alloc(&djrcv_dev->notif_fifo,
> DJ_MAX_NUMBER_NOTIFICATIONS * sizeof(struct dj_report),
> GFP_KERNEL)) {
>
> Where, DJ_MAX_NUMBER_NOTIFICATIONS is 8, and sizeo of(struct dj_report)
> is 15.
>
> Which means it wants to allocate a kfifo buffer which can store 8
> dj_report entries at once. The expected kfifo buffer size would be
> 8 * 15 = 120 then. While, in the end, __kfifo_alloc will turn the
> size to rounddown_power_of_2(120) = 64, and then allocate a buf
> with 64 bytes, which I don't think this is the original author want.
>
> With the new log API, we can do like following:
>
> int kfifo_size_order = order_base_2(DJ_MAX_NUMBER_NOTIFICATIONS *
> sizeof(struct dj_report));
>
> if (kfifo_alloc(&djrcv_dev->notif_fifo, kfifo_size_order, GFP_KERNEL)) {
>
> This make sure we will allocate enough kfifo buffer for holding
> DJ_MAX_NUMBER_NOTIFICATIONS dj_report entries.
Why don't you simply change __kfifo_alloc to round the allocation up
instead of down?
Thanks.
--
Dmitry
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