Re: [PATCH] tcp: assign the sock correctly to an outgoing SYNACK packet

Paul Moore
2013-04-09T15:06:02Z

On Tuesday, April 09, 2013 10:52:17 AM Paul Moore wrote:
> On Tuesday, April 09, 2013 07:31:04 AM Eric Dumazet wrote:
> > On Tue, 2013-04-09 at 10:19 -0400, Paul Moore wrote:
> > > On Tuesday, April 09, 2013 07:00:22 AM Eric Dumazet wrote:
> > > > On Tue, 2013-04-09 at 09:19 -0400, Paul Moore wrote:
> > > > > As Casey already mentioned, if this isn't acceptable please help me
> > > > > understand why.
> > > >
> > > > You see something which is not the reality. If you do such analysis,
> > > > better do it properly, because any change you are going to submit will
> > > > be doubly checked by people who really care.
> > >
> > > I am attempting to do it properly, I simply made a mistake. Ben also
> > > pointed it out. As you wrote yesterday, "Lets go forward".
> > >
> > > After fixing the BITS_PER_LONG problem I looked at it again and it
> > > appears
> > > that by simply replacing the "secmark" field with a blob we retain the
> > > size of the sk_buff as well as the cacheline positions of all the
> > > fields,
> > > e.g. dma_cookie no longer moves cachelines. Thoughts?
> >
> > If you take a look at recent history of changes on sk_buff, you can see
> > we added very recently fields for encapsulation support. These were
> > absolutely wanted for modern operations at datacenter level.
> >
> > This effort might still need new room, so I prefer not filling sk_buff
> > right now.
>
> Has anyone proposed any additional encapsulation patches which need
> additional fields in the sk_buff? Are you aware of any additional
> encapsulation patches which are in progress? When would you consider it
> "safe"?

Another thought.

If we move the "protocol" field after the flags2 bitfield, remove "secmark",
and add the blob before/after "destructor" then we preserve the existing four
byte hole in cacheline #3 for potential use by the encapsulation folks and
move the dma_cookie into cacheline #3 as well which may actually be a good
thing (corrections welcome on this comment). The overall size remains the
same at 256 bytes.

struct sk_buff_test {
struct sk_buff * next; /* 0 8 */
struct sk_buff * prev; /* 8 8 */
ktime_t tstamp; /* 16 8 */
struct sock * sk; /* 24 8 */
struct net_device * dev; /* 32 8 */
char cb[48]; /* 40 48 */
/* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */
long unsigned int _skb_refdst; /* 88 8 */
struct sec_path * sp; /* 96 8 */
unsigned int len; /* 104 4 */
unsigned int data_len; /* 108 4 */
__u16 mac_len; /* 112 2 */
__u16 hdr_len; /* 114 2 */
union {
__wsum csum; /* 4 */
struct {
__u16 csum_start; /* 116 2 */
__u16 csum_offset; /* 118 2 */
}; /* 4 */
}; /* 116 4 */
__u32 priority; /* 120 4 */
int flags1_begin[0]; /* 124 0 */
__u8 local_df:1; /* 124: 7 1 */
__u8 cloned:1; /* 124: 6 1 */
__u8 ip_summed:2; /* 124: 4 1 */
__u8 nohdr:1; /* 124: 3 1 */
__u8 nfctinfo:3; /* 124: 0 1 */
__u8 pkt_type:3; /* 125: 5 1 */
__u8 fclone:2; /* 125: 3 1 */
__u8 ipvs_property:1; /* 125: 2 1 */
__u8 peeked:1; /* 125: 1 1 */
__u8 nf_trace:1; /* 125: 0 1 */

/* XXX 2 bytes hole, try to pack */

/* --- cacheline 2 boundary (128 bytes) --- */
int flags1_end[0]; /* 128 0 */
void * security; /* 128 8 */
void (*destructor)(struct sk_buff *); /* 136
8 */
struct nf_conntrack * nfct; /* 144 8 */
struct sk_buff * nfct_reasm; /* 152 8 */
struct nf_bridge_info * nf_bridge; /* 160 8 */
int skb_iif; /* 168 4 */
__u32 rxhash; /* 172 4 */
__u16 vlan_tci; /* 176 2 */
__u16 tc_index; /* 178 2 */
__u16 tc_verd; /* 180 2 */
__u16 queue_mapping; /* 182 2 */
int flags2_begin[0]; /* 184 0 */
__u8 ndisc_nodetype:2; /* 184: 6 1 */
__u8 pfmemalloc:1; /* 184: 5 1 */
__u8 ooo_okay:1; /* 184: 4 1 */
__u8 l4_rxhash:1; /* 184: 3 1 */
__u8 wifi_acked_valid:1; /* 184: 2 1 */
__u8 wifi_acked:1; /* 184: 1 1 */
__u8 no_fcs:1; /* 184: 0 1 */
__u8 head_frag:1; /* 185: 7 1 */
__u8 encapsulation:1; /* 185: 6 1 */

/* XXX 6 bits hole, try to pack */
/* XXX 2 bytes hole, try to pack */

int flags2_end[0]; /* 188 0 */
__be16 protocol; /* 188 2 */

/* XXX 2 bytes hole, try to pack */

/* --- cacheline 3 boundary (192 bytes) --- */
dma_cookie_t dma_cookie; /* 192 4 */
union {
__u32 mark; /* 4 */
__u32 dropcount; /* 4 */
__u32 reserved_tailroom; /* 4 */
}; /* 196 4 */
sk_buff_data_t inner_transport_header; /* 200 4 */
sk_buff_data_t inner_network_header; /* 204 4 */
sk_buff_data_t transport_header; /* 208 4 */
sk_buff_data_t network_header; /* 212 4 */
sk_buff_data_t mac_header; /* 216 4 */
sk_buff_data_t tail; /* 220 4 */
sk_buff_data_t end; /* 224 4 */

/* XXX 4 bytes hole, try to pack */

unsigned char * head; /* 232 8 */
unsigned char * data; /* 240 8 */
unsigned int truesize; /* 248 4 */
atomic_t users; /* 252 4 */
/* --- cacheline 4 boundary (256 bytes) --- */

/* size: 256, cachelines: 4, members: 62 */
/* sum members: 246, holes: 4, sum holes: 10 */
/* bit holes: 1, sum bit holes: 6 bits */
};

--
paul moore
security and virtualization @ redhat