[PATCHv3 net-next 0/2] net: fix the features flag in sctp_gso_segment

[PATCHv3 net-next 0/2] net: fix the features flag in sctp_gso_segment

[Xin Long]

Patch 1/2 is to improve the code in skb_segment(), and it is needed
by Patch 2/2.

v1->v2:
  - see Patch 1/2.
v2->v3:
  - change Patch 2/2 to the right patch.

Xin Long (2):
  net: move the hsize check to the else block in skb_segment
  sctp: remove the NETIF_F_SG flag before calling skb_segment

 net/core/skbuff.c  | 11 ++++++-----
 net/sctp/offload.c |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

-- 
2.1.0

[PATCHv3 net-next 1/2] net: move the hsize check to the else block in skb_segment

[Xin Long]

After commit 89319d3801d1 ("net: Add frag_list support to skb_segment"),
it goes to process frag_list when !hsize in skb_segment(). However, when
using skb frag_list, sg normally should not be set. In this case, hsize
will be set with len right before !hsize check, then it won't go to
frag_list processing code.

So the right thing to do is move the hsize check to the else block, so
that it won't affect the !hsize check for frag_list processing.

v1->v2:
  - change to do "hsize <= 0" check instead of "!hsize", and also move
    "hsize < 0" into else block, to save some cycles, as Alex suggested.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/core/skbuff.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6039069..e835193 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3894,12 +3894,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 		}
 
 		hsize = skb_headlen(head_skb) - offset;
-		if (hsize < 0)
-			hsize = 0;
-		if (hsize > len || !sg)
-			hsize = len;
 
-		if (!hsize && i >= nfrags && skb_headlen(list_skb) &&
+		if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
 		    (skb_headlen(list_skb) == len || sg)) {
 			BUG_ON(skb_headlen(list_skb) > len);
 
@@ -3942,6 +3938,11 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 			skb_release_head_state(nskb);
 			__skb_push(nskb, doffset);
 		} else {
+			if (hsize > len || !sg)
+				hsize = len;
+			else if (hsize < 0)
+				hsize = 0;
+
 			nskb = __alloc_skb(hsize + doffset + headroom,
 					   GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
 					   NUMA_NO_NODE);
-- 
2.1.0

[PATCHv3 net-next 2/2] sctp: remove the NETIF_F_SG flag before calling skb_segment

[Xin Long]

It makes more sense to clear NETIF_F_SG instead of set it when
calling skb_segment() in sctp_gso_segment(), since SCTP GSO is
using head_skb's fraglist, of which all frags are linear skbs.

This will make SCTP GSO code more understandable.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/offload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/offload.c b/net/sctp/offload.c
index ce281a9..eb874e3 100644
--- a/net/sctp/offload.c
+++ b/net/sctp/offload.c
@@ -68,7 +68,7 @@ static struct sk_buff *sctp_gso_segment(struct sk_buff *skb,
 		goto out;
 	}
 
-	segs = skb_segment(skb, features | NETIF_F_HW_CSUM | NETIF_F_SG);
+	segs = skb_segment(skb, (features | NETIF_F_HW_CSUM) & ~NETIF_F_SG);
 	if (IS_ERR(segs))
 		goto out;
 
-- 
2.1.0

Re: [PATCHv3 net-next 1/2] net: move the hsize check to the else block in skb_segment

[Alexander Duyck]

On Fri, Jan 15, 2021 at 1:36 AM Xin Long <lucien.xin@gmail.com> wrote:
>
> After commit 89319d3801d1 ("net: Add frag_list support to skb_segment"),
> it goes to process frag_list when !hsize in skb_segment(). However, when
> using skb frag_list, sg normally should not be set. In this case, hsize
> will be set with len right before !hsize check, then it won't go to
> frag_list processing code.
>
> So the right thing to do is move the hsize check to the else block, so
> that it won't affect the !hsize check for frag_list processing.
>
> v1->v2:
>   - change to do "hsize <= 0" check instead of "!hsize", and also move
>     "hsize < 0" into else block, to save some cycles, as Alex suggested.
>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>

> ---
>  net/core/skbuff.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 6039069..e835193 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3894,12 +3894,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
>                 }
>
>                 hsize = skb_headlen(head_skb) - offset;
> -               if (hsize < 0)
> -                       hsize = 0;
> -               if (hsize > len || !sg)
> -                       hsize = len;
>
> -               if (!hsize && i >= nfrags && skb_headlen(list_skb) &&
> +               if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
>                     (skb_headlen(list_skb) == len || sg)) {
>                         BUG_ON(skb_headlen(list_skb) > len);
>
> @@ -3942,6 +3938,11 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
>                         skb_release_head_state(nskb);
>                         __skb_push(nskb, doffset);
>                 } else {
> +                       if (hsize > len || !sg)
> +                               hsize = len;
> +                       else if (hsize < 0)
> +                               hsize = 0;
> +
>                         nskb = __alloc_skb(hsize + doffset + headroom,
>                                            GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
>                                            NUMA_NO_NODE);
> --
> 2.1.0
>

Re: [PATCHv3 net-next 1/2] net: move the hsize check to the else block in skb_segment

[Jakub Kicinski]

On Fri, 15 Jan 2021 17:39:02 -0800 Alexander Duyck wrote:
> On Fri, Jan 15, 2021 at 1:36 AM Xin Long <lucien.xin@gmail.com> wrote:
> >
> > After commit 89319d3801d1 ("net: Add frag_list support to skb_segment"),
> > it goes to process frag_list when !hsize in skb_segment(). However, when
> > using skb frag_list, sg normally should not be set. In this case, hsize
> > will be set with len right before !hsize check, then it won't go to
> > frag_list processing code.
> >
> > So the right thing to do is move the hsize check to the else block, so
> > that it won't affect the !hsize check for frag_list processing.
> >
> > v1->v2:
> >   - change to do "hsize <= 0" check instead of "!hsize", and also move
> >     "hsize < 0" into else block, to save some cycles, as Alex suggested.
> >
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>  
> 
> Looks good to me.
> 
> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>

Applied, thanks!