[PATCH net 0/2] SCTP fix

[PATCH net 0/2] SCTP fix

[Daniel Borkmann]

Daniel Borkmann (2):
  net: sctp: spare unnecessary comparison in sctp_trans_elect_best
  net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

 net/sctp/associola.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

-- 
1.7.11.7

[PATCH net 0/2] SCTP fix

[Daniel Borkmann]

Daniel Borkmann (2):
  net: sctp: spare unnecessary comparison in sctp_trans_elect_best
  net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

 net/sctp/associola.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

-- 
1.7.11.7

[PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Daniel Borkmann]

When both transports are the same, we don't have to go down that
road only to realize that we will return the very same transport.
We are guaranteed that curr is always non-NULL. Therefore, just
short-circuit this special case.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/sctp/associola.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index aaafb32..104fae4 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
 {
 	u8 score_curr, score_best;
 
-	if (best == NULL)
+	if (best == NULL || curr == best)
 		return curr;
 
 	score_curr = sctp_trans_score(curr);
-- 
1.7.11.7

[PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Daniel Borkmann]

When both transports are the same, we don't have to go down that
road only to realize that we will return the very same transport.
We are guaranteed that curr is always non-NULL. Therefore, just
short-circuit this special case.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/sctp/associola.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index aaafb32..104fae4 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
 {
 	u8 score_curr, score_best;
 
-	if (best = NULL)
+	if (best = NULL || curr = best)
 		return curr;
 
 	score_curr = sctp_trans_score(curr);
-- 
1.7.11.7

[PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Daniel Borkmann]

In SCTP, selection of active (T.ACT) and retransmission (T.RET)
transports is being done whenever transport control operations
(UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().

Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
sctp_select_active_and_retran_path selection") have both improved
it towards a more fine-grained and optimal path selection.

Currently, the selection algorithm for T.ACT and T.RET is as follows:

1) Elect the two most recently used ACTIVE transports T1, T2 for
   T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used
2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set
   T.ACT<-T.PRI and T.RET<-T1
3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1
4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where
   T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI

Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and
T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is
still slightly suboptimal as it can lead to the following scenario:

Setup:
        <A>                                <B>
    T1: p1p1 (10.0.10.10) <==>  .'`)  <==> p1p1 (10.0.10.12)  <= T.PRI
    T2: p1p2 (10.0.10.20) <==> (_ . ) <==> p1p2 (10.0.10.22)

    net.sctp.rto_min = 1000
    net.sctp.path_max_retrans = 2
    net.sctp.pf_retrans = 0
    net.sctp.hb_interval = 1000

T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to
link flapping). Here, the first time transmission is sent over PF path
T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks
are sent over the INACTIVE path T1 (T.PRI), which is not good.

After the patch, it's choosing better transports in both cases by
modifying step 4):

4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is
   the most recently used (if avail) in PF, set T.RET<-T.ACT_new

This will still select a best possible path in PF if available (which
can also include T.PRI/T.RET), and set both T.ACT/T.RET to it.

In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE
as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just
for a very short while before going back ACTIVE, it will guarantee that
this path will be reselected for T.ACT/T.RET since T3 (PF) is not
available.

Previously, this was not possible, as we would only select between T.PRI
and T.RET, and a possible T3 would be NULL due to the fact that we have
just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE
and would select a suboptimal path when T.PRI/T.RET have worse properties.

In the case that T.ACT_old permanently went to INACTIVE during this
transition and there's no PF path available, plus T.PRI and T.RET are
INACTIVE as well, we would now camp on T.ACT_old, but if everything is
being INACTIVE there's really not much we can do except hoping for a
successful HB to bring one of the transports back up again and, thus
cause a new selection through sctp_assoc_control_transport().

Now both tests work fine:

Case 1:

 1. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

 2. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(PF)

 3. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(INACTIVE)

 5. T1 S(PF) T.ACT, T.RET
    T2 S(INACTIVE)

[ 5.1 T1 S(INACTIVE) T.ACT, T.RET
      T2 S(INACTIVE) ]

 6. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(INACTIVE)

 7. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

Case 2:

 1. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

 2. T1 S(PF)
    T2 S(ACTIVE) T.ACT, T.RET

 3. T1 S(INACTIVE)
    T2 S(ACTIVE) T.ACT, T.RET

 5. T1 S(INACTIVE)
    T2 S(PF) T.ACT, T.RET

[ 5.1 T1 S(INACTIVE)
      T2 S(INACTIVE) T.ACT, T.RET ]

 6. T1 S(INACTIVE)
    T2 S(ACTIVE) T.ACT, T.RET

 7. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/sctp/associola.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 104fae4..a88b852 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
 		trans_sec = trans_pri;
 
 	/* If we failed to find a usable transport, just camp on the
-	 * primary or retran, even if they are inactive, if possible
-	 * pick a PF iff it's the better choice.
+	 * active or pick a PF iff it's the better choice.
 	 */
 	if (trans_pri == NULL) {
-		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
-						  asoc->peer.retran_path);
-		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
-		trans_sec = asoc->peer.primary_path;
+		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
+		trans_sec = trans_pri;
 	}
 
 	/* Set the active and retran transports. */
-- 
1.7.11.7

[PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Daniel Borkmann]

In SCTP, selection of active (T.ACT) and retransmission (T.RET)
transports is being done whenever transport control operations
(UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().

Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
sctp_select_active_and_retran_path selection") have both improved
it towards a more fine-grained and optimal path selection.

Currently, the selection algorithm for T.ACT and T.RET is as follows:

1) Elect the two most recently used ACTIVE transports T1, T2 for
   T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used
2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set
   T.ACT<-T.PRI and T.RET<-T1
3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1
4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where
   T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI

Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and
T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is
still slightly suboptimal as it can lead to the following scenario:

Setup:
        <A>                                <B>
    T1: p1p1 (10.0.10.10) <=>  .'`)  <=> p1p1 (10.0.10.12)  <= T.PRI
    T2: p1p2 (10.0.10.20) <=> (_ . ) <=> p1p2 (10.0.10.22)

    net.sctp.rto_min = 1000
    net.sctp.path_max_retrans = 2
    net.sctp.pf_retrans = 0
    net.sctp.hb_interval = 1000

T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to
link flapping). Here, the first time transmission is sent over PF path
T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks
are sent over the INACTIVE path T1 (T.PRI), which is not good.

After the patch, it's choosing better transports in both cases by
modifying step 4):

4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is
   the most recently used (if avail) in PF, set T.RET<-T.ACT_new

This will still select a best possible path in PF if available (which
can also include T.PRI/T.RET), and set both T.ACT/T.RET to it.

In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE
as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just
for a very short while before going back ACTIVE, it will guarantee that
this path will be reselected for T.ACT/T.RET since T3 (PF) is not
available.

Previously, this was not possible, as we would only select between T.PRI
and T.RET, and a possible T3 would be NULL due to the fact that we have
just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE
and would select a suboptimal path when T.PRI/T.RET have worse properties.

In the case that T.ACT_old permanently went to INACTIVE during this
transition and there's no PF path available, plus T.PRI and T.RET are
INACTIVE as well, we would now camp on T.ACT_old, but if everything is
being INACTIVE there's really not much we can do except hoping for a
successful HB to bring one of the transports back up again and, thus
cause a new selection through sctp_assoc_control_transport().

Now both tests work fine:

Case 1:

 1. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

 2. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(PF)

 3. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(INACTIVE)

 5. T1 S(PF) T.ACT, T.RET
    T2 S(INACTIVE)

[ 5.1 T1 S(INACTIVE) T.ACT, T.RET
      T2 S(INACTIVE) ]

 6. T1 S(ACTIVE) T.ACT, T.RET
    T2 S(INACTIVE)

 7. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

Case 2:

 1. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

 2. T1 S(PF)
    T2 S(ACTIVE) T.ACT, T.RET

 3. T1 S(INACTIVE)
    T2 S(ACTIVE) T.ACT, T.RET

 5. T1 S(INACTIVE)
    T2 S(PF) T.ACT, T.RET

[ 5.1 T1 S(INACTIVE)
      T2 S(INACTIVE) T.ACT, T.RET ]

 6. T1 S(INACTIVE)
    T2 S(ACTIVE) T.ACT, T.RET

 7. T1 S(ACTIVE) T.ACT
    T2 S(ACTIVE) T.RET

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/sctp/associola.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 104fae4..a88b852 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
 		trans_sec = trans_pri;
 
 	/* If we failed to find a usable transport, just camp on the
-	 * primary or retran, even if they are inactive, if possible
-	 * pick a PF iff it's the better choice.
+	 * active or pick a PF iff it's the better choice.
 	 */
 	if (trans_pri = NULL) {
-		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
-						  asoc->peer.retran_path);
-		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
-		trans_sec = asoc->peer.primary_path;
+		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
+		trans_sec = trans_pri;
 	}
 
 	/* Set the active and retran transports. */
-- 
1.7.11.7

Re: [PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Neil Horman]

On Fri, Aug 22, 2014 at 01:03:29PM +0200, Daniel Borkmann wrote:
> When both transports are the same, we don't have to go down that
> road only to realize that we will return the very same transport.
> We are guaranteed that curr is always non-NULL. Therefore, just
> short-circuit this special case.
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> ---
>  net/sctp/associola.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index aaafb32..104fae4 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
>  {
>  	u8 score_curr, score_best;
>  
> -	if (best == NULL)
> +	if (best == NULL || curr == best)
>  		return curr;
>  
>  	score_curr = sctp_trans_score(curr);
Acked-by: Neil Horman <nhorman@tuxdriver.com>

> -- 
> 1.7.11.7
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Neil Horman]

On Fri, Aug 22, 2014 at 01:03:29PM +0200, Daniel Borkmann wrote:
> When both transports are the same, we don't have to go down that
> road only to realize that we will return the very same transport.
> We are guaranteed that curr is always non-NULL. Therefore, just
> short-circuit this special case.
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> ---
>  net/sctp/associola.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index aaafb32..104fae4 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
>  {
>  	u8 score_curr, score_best;
>  
> -	if (best = NULL)
> +	if (best = NULL || curr = best)
>  		return curr;
>  
>  	score_curr = sctp_trans_score(curr);
Acked-by: Neil Horman <nhorman@tuxdriver.com>

> -- 
> 1.7.11.7
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Neil Horman]

On Fri, Aug 22, 2014 at 01:03:30PM +0200, Daniel Borkmann wrote:
> In SCTP, selection of active (T.ACT) and retransmission (T.RET)
> transports is being done whenever transport control operations
> (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().
> 
> Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
> path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
> sctp_select_active_and_retran_path selection") have both improved
> it towards a more fine-grained and optimal path selection.
> 
> Currently, the selection algorithm for T.ACT and T.RET is as follows:
> 
> 1) Elect the two most recently used ACTIVE transports T1, T2 for
>    T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used
> 2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set
>    T.ACT<-T.PRI and T.RET<-T1
> 3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1
> 4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where
>    T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI
> 
> Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and
> T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is
> still slightly suboptimal as it can lead to the following scenario:
> 
> Setup:
>         <A>                                <B>
>     T1: p1p1 (10.0.10.10) <==>  .'`)  <==> p1p1 (10.0.10.12)  <= T.PRI
>     T2: p1p2 (10.0.10.20) <==> (_ . ) <==> p1p2 (10.0.10.22)
> 
>     net.sctp.rto_min = 1000
>     net.sctp.path_max_retrans = 2
>     net.sctp.pf_retrans = 0
>     net.sctp.hb_interval = 1000
> 
> T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to
> link flapping). Here, the first time transmission is sent over PF path
> T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks
> are sent over the INACTIVE path T1 (T.PRI), which is not good.
> 
> After the patch, it's choosing better transports in both cases by
> modifying step 4):
> 
> 4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is
>    the most recently used (if avail) in PF, set T.RET<-T.ACT_new
> 
> This will still select a best possible path in PF if available (which
> can also include T.PRI/T.RET), and set both T.ACT/T.RET to it.
> 
> In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE
> as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just
> for a very short while before going back ACTIVE, it will guarantee that
> this path will be reselected for T.ACT/T.RET since T3 (PF) is not
> available.
> 
> Previously, this was not possible, as we would only select between T.PRI
> and T.RET, and a possible T3 would be NULL due to the fact that we have
> just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE
> and would select a suboptimal path when T.PRI/T.RET have worse properties.
> 
> In the case that T.ACT_old permanently went to INACTIVE during this
> transition and there's no PF path available, plus T.PRI and T.RET are
> INACTIVE as well, we would now camp on T.ACT_old, but if everything is
> being INACTIVE there's really not much we can do except hoping for a
> successful HB to bring one of the transports back up again and, thus
> cause a new selection through sctp_assoc_control_transport().
> 
> Now both tests work fine:
> 
> Case 1:
> 
>  1. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
>  2. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(PF)
> 
>  3. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
>  5. T1 S(PF) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
> [ 5.1 T1 S(INACTIVE) T.ACT, T.RET
>       T2 S(INACTIVE) ]
> 
>  6. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
>  7. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
> Case 2:
> 
>  1. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
>  2. T1 S(PF)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  3. T1 S(INACTIVE)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  5. T1 S(INACTIVE)
>     T2 S(PF) T.ACT, T.RET
> 
> [ 5.1 T1 S(INACTIVE)
>       T2 S(INACTIVE) T.ACT, T.RET ]
> 
>  6. T1 S(INACTIVE)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  7. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> ---
>  net/sctp/associola.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 104fae4..a88b852 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
>  		trans_sec = trans_pri;
>  
>  	/* If we failed to find a usable transport, just camp on the
> -	 * primary or retran, even if they are inactive, if possible
> -	 * pick a PF iff it's the better choice.
> +	 * active or pick a PF iff it's the better choice.
>  	 */
>  	if (trans_pri == NULL) {
> -		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
> -						  asoc->peer.retran_path);
> -		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
> -		trans_sec = asoc->peer.primary_path;
> +		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
> +		trans_sec = trans_pri;
>  	}
>  
>  	/* Set the active and retran transports. */
> -- 
> 1.7.11.7
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
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> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>

Re: [PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Neil Horman]

On Fri, Aug 22, 2014 at 01:03:30PM +0200, Daniel Borkmann wrote:
> In SCTP, selection of active (T.ACT) and retransmission (T.RET)
> transports is being done whenever transport control operations
> (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().
> 
> Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
> path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
> sctp_select_active_and_retran_path selection") have both improved
> it towards a more fine-grained and optimal path selection.
> 
> Currently, the selection algorithm for T.ACT and T.RET is as follows:
> 
> 1) Elect the two most recently used ACTIVE transports T1, T2 for
>    T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used
> 2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set
>    T.ACT<-T.PRI and T.RET<-T1
> 3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1
> 4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where
>    T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI
> 
> Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and
> T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is
> still slightly suboptimal as it can lead to the following scenario:
> 
> Setup:
>         <A>                                <B>
>     T1: p1p1 (10.0.10.10) <=>  .'`)  <=> p1p1 (10.0.10.12)  <= T.PRI
>     T2: p1p2 (10.0.10.20) <=> (_ . ) <=> p1p2 (10.0.10.22)
> 
>     net.sctp.rto_min = 1000
>     net.sctp.path_max_retrans = 2
>     net.sctp.pf_retrans = 0
>     net.sctp.hb_interval = 1000
> 
> T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to
> link flapping). Here, the first time transmission is sent over PF path
> T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks
> are sent over the INACTIVE path T1 (T.PRI), which is not good.
> 
> After the patch, it's choosing better transports in both cases by
> modifying step 4):
> 
> 4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is
>    the most recently used (if avail) in PF, set T.RET<-T.ACT_new
> 
> This will still select a best possible path in PF if available (which
> can also include T.PRI/T.RET), and set both T.ACT/T.RET to it.
> 
> In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE
> as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just
> for a very short while before going back ACTIVE, it will guarantee that
> this path will be reselected for T.ACT/T.RET since T3 (PF) is not
> available.
> 
> Previously, this was not possible, as we would only select between T.PRI
> and T.RET, and a possible T3 would be NULL due to the fact that we have
> just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE
> and would select a suboptimal path when T.PRI/T.RET have worse properties.
> 
> In the case that T.ACT_old permanently went to INACTIVE during this
> transition and there's no PF path available, plus T.PRI and T.RET are
> INACTIVE as well, we would now camp on T.ACT_old, but if everything is
> being INACTIVE there's really not much we can do except hoping for a
> successful HB to bring one of the transports back up again and, thus
> cause a new selection through sctp_assoc_control_transport().
> 
> Now both tests work fine:
> 
> Case 1:
> 
>  1. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
>  2. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(PF)
> 
>  3. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
>  5. T1 S(PF) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
> [ 5.1 T1 S(INACTIVE) T.ACT, T.RET
>       T2 S(INACTIVE) ]
> 
>  6. T1 S(ACTIVE) T.ACT, T.RET
>     T2 S(INACTIVE)
> 
>  7. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
> Case 2:
> 
>  1. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
>  2. T1 S(PF)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  3. T1 S(INACTIVE)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  5. T1 S(INACTIVE)
>     T2 S(PF) T.ACT, T.RET
> 
> [ 5.1 T1 S(INACTIVE)
>       T2 S(INACTIVE) T.ACT, T.RET ]
> 
>  6. T1 S(INACTIVE)
>     T2 S(ACTIVE) T.ACT, T.RET
> 
>  7. T1 S(ACTIVE) T.ACT
>     T2 S(ACTIVE) T.RET
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> ---
>  net/sctp/associola.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 104fae4..a88b852 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
>  		trans_sec = trans_pri;
>  
>  	/* If we failed to find a usable transport, just camp on the
> -	 * primary or retran, even if they are inactive, if possible
> -	 * pick a PF iff it's the better choice.
> +	 * active or pick a PF iff it's the better choice.
>  	 */
>  	if (trans_pri = NULL) {
> -		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
> -						  asoc->peer.retran_path);
> -		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
> -		trans_sec = asoc->peer.primary_path;
> +		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
> +		trans_sec = trans_pri;
>  	}
>  
>  	/* Set the active and retran transports. */
> -- 
> 1.7.11.7
> 
> --
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> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>

Re: [PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Vlad Yasevich]

On 08/22/2014 07:03 AM, Daniel Borkmann wrote:
> When both transports are the same, we don't have to go down that
> road only to realize that we will return the very same transport.
> We are guaranteed that curr is always non-NULL. Therefore, just
> short-circuit this special case.
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

-vlad

> ---
>  net/sctp/associola.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index aaafb32..104fae4 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
>  {
>  	u8 score_curr, score_best;
>  
> -	if (best == NULL)
> +	if (best == NULL || curr == best)
>  		return curr;
>  
>  	score_curr = sctp_trans_score(curr);
> 

Re: [PATCH net 1/2] net: sctp: spare unnecessary comparison in sctp_trans_elect_best

[Vlad Yasevich]

On 08/22/2014 07:03 AM, Daniel Borkmann wrote:
> When both transports are the same, we don't have to go down that
> road only to realize that we will return the very same transport.
> We are guaranteed that curr is always non-NULL. Therefore, just
> short-circuit this special case.
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

-vlad

> ---
>  net/sctp/associola.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index aaafb32..104fae4 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1245,7 +1245,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
>  {
>  	u8 score_curr, score_best;
>  
> -	if (best = NULL)
> +	if (best = NULL || curr = best)
>  		return curr;
>  
>  	score_curr = sctp_trans_score(curr);
> 

Re: [PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Vlad Yasevich]

On 08/22/2014 07:03 AM, Daniel Borkmann wrote:
> In SCTP, selection of active (T.ACT) and retransmission (T.RET)
> transports is being done whenever transport control operations
> (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().
> 
> Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
> path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
> sctp_select_active_and_retran_path selection") have both improved
> it towards a more fine-grained and optimal path selection.
> 
.. snip excellent changelog description ...

>     T2 S(ACTIVE) T.RET
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

> ---
>  net/sctp/associola.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 104fae4..a88b852 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
>  		trans_sec = trans_pri;
>  
>  	/* If we failed to find a usable transport, just camp on the
> -	 * primary or retran, even if they are inactive, if possible
> -	 * pick a PF iff it's the better choice.
> +	 * active or pick a PF iff it's the better choice.
>  	 */
>  	if (trans_pri == NULL) {
> -		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
> -						  asoc->peer.retran_path);
> -		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
> -		trans_sec = asoc->peer.primary_path;
> +		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
> +		trans_sec = trans_pri;
>  	}
>  
>  	/* Set the active and retran transports. */
> 

Re: [PATCH net 2/2] net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

[Vlad Yasevich]

On 08/22/2014 07:03 AM, Daniel Borkmann wrote:
> In SCTP, selection of active (T.ACT) and retransmission (T.RET)
> transports is being done whenever transport control operations
> (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport().
> 
> Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission
> path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve
> sctp_select_active_and_retran_path selection") have both improved
> it towards a more fine-grained and optimal path selection.
> 
.. snip excellent changelog description ...

>     T2 S(ACTIVE) T.RET
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

> ---
>  net/sctp/associola.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 104fae4..a88b852 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc)
>  		trans_sec = trans_pri;
>  
>  	/* If we failed to find a usable transport, just camp on the
> -	 * primary or retran, even if they are inactive, if possible
> -	 * pick a PF iff it's the better choice.
> +	 * active or pick a PF iff it's the better choice.
>  	 */
>  	if (trans_pri = NULL) {
> -		trans_pri = sctp_trans_elect_best(asoc->peer.primary_path,
> -						  asoc->peer.retran_path);
> -		trans_pri = sctp_trans_elect_best(trans_pri, trans_pf);
> -		trans_sec = asoc->peer.primary_path;
> +		trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf);
> +		trans_sec = trans_pri;
>  	}
>  
>  	/* Set the active and retran transports. */
> 

Re: [PATCH net 0/2] SCTP fix

[David Miller]

From: Daniel Borkmann <dborkman@redhat.com>
Date: Fri, 22 Aug 2014 13:03:28 +0200

> Daniel Borkmann (2):
>   net: sctp: spare unnecessary comparison in sctp_trans_elect_best
>   net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

Both applied, thanks.

 

Re: [PATCH net 0/2] SCTP fix

[David Miller]

From: Daniel Borkmann <dborkman@redhat.com>
Date: Fri, 22 Aug 2014 13:03:28 +0200

> Daniel Borkmann (2):
>   net: sctp: spare unnecessary comparison in sctp_trans_elect_best
>   net: sctp: fix suboptimal edge-case on non-active active/retrans path selection

Both applied, thanks.