On Thu, Sep 18, 2014 at 11:19 AM, Johan Hovold <jo...@kernel.org> wrote:
> On Wed, Sep 17, 2014 at 01:07:51PM +0300, Octavian Purdila wrote:
>> On Wed, Sep 17, 2014 at 12:44 PM, Johan Hovold <jo...@kernel.org> wrote:
>>
>> <snip>
>>
>> >> + /*
>> >> + * Buffer to hold the packet for read or write transfers. One
>> >> + * is enough since we can't have multiple transfers in
>> >> + * parallel on the i2c adapter.
>> >> + */
>> >> + union {
>> >> + struct {
>> >> + u8 port;
>> >> + u8 addr;
>> >> + u8 mem_addr_len;
>> >> + __le32 mem_addr;
>> >> + __le16 buf_len;
>> >> + u8 buf[DLN2_I2C_MAX_XFER_SIZE];
>> >> + } __packed tx;
>> >> + struct {
>> >> + __le16 buf_len;
>> >> + u8 buf[DLN2_I2C_MAX_XFER_SIZE];
>> >> + } __packed rx;
>> >> + } buf;
>> >
>> > While this works in this case due to the extra copy you do in
>> > dln2_transfer, allocating buffers that would (generally) be used for DMA
>> > transfers as part of a larger structure is a recipe for trouble.
>> >
>> > It's probably better to allocate separately, if only to prevent people
>> > from thinking there might be a bug here.
>> >
>>
>> Just to make sure I understand this, what could the issues be? The
>> buffers not being aligned or not allocated in continuous physical
>> memory?
>
> Yes, the buffer (and any subsequent field) would have to be cache-line
> aligned to avoid corruption due to cache-line sharing on some systems.
>
Ah, ok, makes sense now. But is it safe to use kmalloc() in this case?
Does kmalloc() prevent cache line sharing?
>> <snip>
>>
>> >> +
>> >> + rx_buf_len = le16_to_cpu(dln2->buf.rx.buf_len);
>> >> + if (rx_len < rx_buf_len + sizeof(dln2->buf.rx.buf_len))
>> >> + return -EPROTO;
>> >> +
>> >> + if (data_len > rx_buf_len)
>> >> + data_len = rx_buf_len;
>> >
>> > You're still not checking that the received data does not overflow the
>> > supplied buffer as I already commented on v3.
>> >
>> >> +
>> >> + memcpy(data, dln2->buf.rx.buf, data_len);
>> >> +
>> >> + return data_len;
>> >> +}
>>
>> Hmm, perhaps I am missing something, but we never transfer more then
>> data_len, where data_len is the size of the buffer supplied by the
>> user.
>
> That is the amount of data you request from the device, but you never
> check how much is actually returned.
>
Actually we check the receive buffer size here:
if (data_len > rx_buf_len)
data_len = rx_buf_len;
rx_buf_len is the i2c received payload size while rx_len is the length
of received message
> You really should clean up the error handling of this function as it is
> currently not very readable.
>
Perhaps adding some comments similar to the the explanation above would help?
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