Hi YongSu,
I'm stripping "linux-kernel@xxxxxxxxxxxxxxx". Hopefully that will help.
Developers may receive hundreds of e-mails every day, and CC'ing too
many lists may cause the e-mail to get ignored.
Mauro, CC'ed: Can we have a comment on this issue from some Linux Media
developers having commit access?
--HPS
On 9/13/22 10:36, 유용수 wrote:
Dear Hans Petter Selasky
I understood your points.
Thank you for your kind explanation
I found that the buffer size is 65535 like below source code.
The 65535 is not the power of two.
So it can still be a problem.
...
#define RX_BUFFER_SIZE 65535
...
rxbuf = vmalloc(RX_BUFFER_SIZE);
...
dvb_ringbuffer_init(&ca->slot_info[slot].rx_buffer, rxbuf, RX_BUFFER_SIZE);
}
...
2022년 9월 12일 (월) 오후 9:36, Hans Petter Selasky <hps@xxxxxxxxxxx>님이 작성:
Hi Mauro and YongSu,
Answering my own question: The reason nobody has triggered this yet, is
because the buffer size used is power of two. Because unsigned modulus
is used, the result becomes correct. See below. But if non-power of two
ring-buffer is used, then the result becomes incorrect. There is no
block for non-power of two sized buffers. See:
https://github.com/search?q=dvb_set_pesfilter&type=code
cat << EOF > testX.c
#include <stdio.h>
int
main()
{
int consumed_old;
int consumed_fix;
size_t idx = 3;
ssize_t pread = 15;
ssize_t size = 256;
consumed_old = (idx - pread) % size;
consumed_fix = (idx - pread);
if (consumed_fix < 0)
consumed_fix += size;
printf("old=%d new=%d size=%zd\n", consumed_old, consumed_fix, size);
size = 254;
consumed_old = (idx - pread) % size;
consumed_fix = (idx - pread);
if (consumed_fix < 0)
consumed_fix += size;
printf("old=%d new=%d size=%zd\n", consumed_old, consumed_fix, size);
return (0);
}
EOF
cc testX.c && ./a.out
old=244 new=244 size=256
old=244 new=242 size=254
So either push the suggested fix, or block non-power of two buffer sizes!
Best regards,
--HPS
