On 03/27/2018 10:41 AM, Prashant Bhole wrote:
> On 3/27/2018 12:15 PM, John Fastabend wrote:
>> On 03/25/2018 11:54 PM, Prashant Bhole wrote:
>>> When CONFIG_DEBUG_SG is set, sg->sg_magic is initialized to SG_MAGIC,
>>> when sg table is initialized using sg_init_table(). Magic is checked
>>> while navigating the scatterlist. We hit BUG_ON when magic check is
>>> failed.
>>>
>>> Fixed following things:
>>> - Initialization of sg table in bpf_tcp_sendpage() was missing,
>>> initialized it using sg_init_table()
>>>
>>> - bpf_tcp_sendmsg() initializes sg table using sg_init_table() before
>>> entering the loop, but further consumed sg entries are initialized
>>> using memset. Fixed it by replacing memset with sg_init_table() in
>>> function bpf_tcp_push()
>>>
>>> Signed-off-by: Prashant Bhole <bhole_prashant...@lab.ntt.co.jp>
>>> ---
>>> kernel/bpf/sockmap.c | 11 +++++++----
>>> 1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
>>> index 69c5bccabd22..8a848a99d768 100644
>>> --- a/kernel/bpf/sockmap.c
>>> +++ b/kernel/bpf/sockmap.c
>>> @@ -312,7 +312,7 @@ static int bpf_tcp_push(struct sock *sk, int
>>> apply_bytes,
>>> md->sg_start++;
>>> if (md->sg_start == MAX_SKB_FRAGS)
>>> md->sg_start = 0;
>>> - memset(sg, 0, sizeof(*sg));
>>> + sg_init_table(sg, 1);
>>
>> Looks OK here.
>>
>>> if (md->sg_start == md->sg_end)
>>> break;
>>> @@ -763,10 +763,14 @@ static int bpf_tcp_sendpage(struct sock *sk, struct
>>> page *page,
>>> lock_sock(sk);
>>> - if (psock->cork_bytes)
>>> + if (psock->cork_bytes) {
>>> m = psock->cork;
>>> - else
>>> + sg = &m->sg_data[m->sg_end];
>>> + } else {
>>> m = &md;
>>> + sg = m->sg_data;
>>> + sg_init_table(sg, MAX_SKB_FRAGS);
>>
>> sg_init_table() does an unnecessary memset() though. We
>> probably either want a new scatterlist API or just open
>> code this,
>>
>> #ifdef CONFIG_DEBUG_SG
>> {
>> unsigned int i;
>> for (i = 0; i < nents; i++)
>> sgl[i].sg_magic = SG_MAGIC;
>> }
>
> Similar sg_init_table() is present in bpf_tcp_sendmsg().
> I agree that it causes unnecessary memset, but I don't agree with open coded
> fix.
But then lets fix is properly and add a static inline helper to the
include/linux/scatterlist.h header like ...
static inline void sg_init_debug_marker(struct scatterlist *sgl,
unsigned int nents)
{
#ifdef CONFIG_DEBUG_SG
unsigned int i;
for (i = 0; i < nents; i++)
sgl[i].sg_magic = SG_MAGIC;
#endif
}
... and reuse it in all the places that would otherwise open-code this,
as well as sg_init_table():
void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
memset(sgl, 0, sizeof(*sgl) * nents);
sg_init_debug_marker(sgl, nents);
sg_mark_end(&sgl[nents - 1]);
}
This would be a lot cleaner than having this duplicated in various places.
Thanks,
Daniel
