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sctp: fix sk_wmem_queued and use it to check for writable space

PATCH In review Xin Long 2 participants 4 messages Oct 16, 2018 – Oct 18, 2018

Subsystems (3)
Networking Network drivers SCTP protocol
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Xin Long

author maintainer
#0 lore raw

cover sctp: fix sk_wmem_queued and use it to check for writable space

sctp doesn't count and use asoc sndbuf_used, sk sk_wmem_alloc and sk_wmem_queued properly, which also causes some problem.

This patchset is to improve it.

Xin Long (2):
sctp: count both sk and asoc sndbuf with skb truesize and sctp_chunk
size
sctp: use sk_wmem_queued to check for writable space

 include/net/sctp/constants.h |  5 ----
 net/sctp/outqueue.c          |  8 ++----
 net/sctp/socket.c            | 59 +++++++++++---------------------------------
 3 files changed, 17 insertions(+), 55 deletions(-)
Signature · 1 line
2.1.0
author maintainer
#1 lore raw

PATCH 1/2 sctp: count both sk and asoc sndbuf with skb truesize and sctp_chunk size

Now it's confusing that asoc sndbuf_used is doing memory accounting with SCTP_DATA_SNDSIZE(chunk) + sizeof(sk_buff) + sizeof(sctp_chunk) while sk sk_wmem_alloc is doing that with skb->truesize + sizeof(sctp_chunk).

It also causes sctp_prsctp_prune to count with a wrong freed memory when sndbuf_policy is not set.

To make this right and also keep consistent between asoc sndbuf_used, sk sk_wmem_alloc and sk_wmem_queued, use skb->truesize + sizeof(sctp_chunk) for them.

Signed-off-by Xin Long <[email protected]>
---
 include/net/sctp/constants.h |  5 -----
 net/sctp/outqueue.c          |  8 ++------
 net/sctp/socket.c            | 21 ++++++---------------
 3 files changed, 8 insertions(+), 26 deletions(-)
include/net/sctp/constants.h +0 -5
index 86f034b..8dadc74 100644
@@ -148,11 +148,6 @@ SCTP_SUBTYPE_CONSTRUCTOR(PRIMITIVE,	enum sctp_event_primitive, primitive)
 #define sctp_chunk_is_data(a) (a->chunk_hdr->type = SCTP_CID_DATA || \
 			       a->chunk_hdr->type = SCTP_CID_I_DATA)
 
-/* Calculate the actual data size in a data chunk */
-#define SCTP_DATA_SNDSIZE(c) ((int)((unsigned long)(c->chunk_end) - \
-				    (unsigned long)(c->chunk_hdr) - \
-				    sctp_datachk_len(&c->asoc->stream)))
-
 /* Internal error codes */
 enum sctp_ierror {
 	SCTP_IERROR_NO_ERROR	        = 0,
net/sctp/outqueue.c +2 -6
index 42191ed..9cb854b 100644
@@ -385,9 +385,7 @@ static int sctp_prsctp_prune_sent(struct sctp_association *asoc,
 			asoc->outqueue.outstanding_bytes -= sctp_data_size(chk);
 		}
 
-		msg_len -= SCTP_DATA_SNDSIZE(chk) +
-			   sizeof(struct sk_buff) +
-			   sizeof(struct sctp_chunk);
+		msg_len -= chk->skb->truesize + sizeof(struct sctp_chunk);
 		if (msg_len <= 0)
 			break;
 	}

@@ -421,9 +419,7 @@ static int sctp_prsctp_prune_unsent(struct sctp_association *asoc,
 			streamout->ext->abandoned_unsent[SCTP_PR_INDEX(PRIO)]++;
 		}
 
-		msg_len -= SCTP_DATA_SNDSIZE(chk) +
-			   sizeof(struct sk_buff) +
-			   sizeof(struct sctp_chunk);
+		msg_len -= chk->skb->truesize + sizeof(struct sctp_chunk);
 		sctp_chunk_free(chk);
 		if (msg_len <= 0)
 			break;
net/sctp/socket.c +6 -15
index f73e9d3..c6f2950 100644
@@ -166,12 +166,9 @@ static inline void sctp_set_owner_w(struct sctp_chunk *chunk)
 	/* Save the chunk pointer in skb for sctp_wfree to use later.  */
 	skb_shinfo(chunk->skb)->destructor_arg = chunk;
 
-	asoc->sndbuf_used += SCTP_DATA_SNDSIZE(chunk) +
-				sizeof(struct sk_buff) +
-				sizeof(struct sctp_chunk);
-
 	refcount_add(sizeof(struct sctp_chunk), &sk->sk_wmem_alloc);
-	sk->sk_wmem_queued += chunk->skb->truesize;
+	asoc->sndbuf_used += chunk->skb->truesize + sizeof(struct sctp_chunk);
+	sk->sk_wmem_queued += chunk->skb->truesize + sizeof(struct sctp_chunk);
 	sk_mem_charge(sk, chunk->skb->truesize);
 }
 

@@ -8460,17 +8457,11 @@ static void sctp_wfree(struct sk_buff *skb)
 	struct sctp_association *asoc = chunk->asoc;
 	struct sock *sk = asoc->base.sk;
 
-	asoc->sndbuf_used -= SCTP_DATA_SNDSIZE(chunk) +
-				sizeof(struct sk_buff) +
-				sizeof(struct sctp_chunk);
-
-	WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk), &sk->sk_wmem_alloc));
-
-	/*
-	 * This undoes what is done via sctp_set_owner_w and sk_mem_charge
-	 */
-	sk->sk_wmem_queued   -= skb->truesize;
 	sk_mem_uncharge(sk, skb->truesize);
+	sk->sk_wmem_queued -= skb->truesize + sizeof(struct sctp_chunk);
+	asoc->sndbuf_used -= skb->truesize + sizeof(struct sctp_chunk);
+	WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk),
+				      &sk->sk_wmem_alloc));
 
 	if (chunk->shkey) {
 		struct sctp_shared_key *shkey = chunk->shkey;
Signature · 1 line
2.1.0
author maintainer
#2 lore raw

PATCH 2/2 sctp: use sk_wmem_queued to check for writable space

sk->sk_wmem_queued is used to count the size of chunks in out queue while sk->sk_wmem_alloc is for counting the size of chunks has been sent. sctp is increasing both of them before enqueuing the chunks, and using sk->sk_wmem_alloc to check for writable space.

However, sk_wmem_alloc is also increased by 1 for the skb allocked for sending in sctp_packet_transmit() but it will not wake up the waiters when sk_wmem_alloc is decreased in this skb's destructor.

If msg size is equal to sk_sndbuf and sendmsg is waiting for sndbuf, the check 'msg_len <= sctp_wspace(asoc)' in sctp_wait_for_sndbuf() will keep waiting if there's a skb allocked in sctp_packet_transmit, and later even if this skb got freed, the waiting thread will never get waked up.

This issue has been there since very beginning, so we change to use sk->sk_wmem_queued to check for writable space as sk_wmem_queued is not increased for the skb allocked for sending, also as TCP does.

SOCK_SNDBUF_LOCK check is also removed here as it's for tx buf auto tuning which I will add in another patch.

Signed-off-by Xin Long <[email protected]>
---
 net/sctp/socket.c | 38 +++++++++-----------------------------
 1 file changed, 9 insertions(+), 29 deletions(-)
net/sctp/socket.c +9 -29
index c6f2950..111ebd8 100644
@@ -83,7 +83,7 @@
 #include <net/sctp/stream_sched.h>
 
 /* Forward declarations for internal helper functions. */
-static int sctp_writeable(struct sock *sk);
+static bool sctp_writeable(struct sock *sk);
 static void sctp_wfree(struct sk_buff *skb);
 static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
 				size_t msg_len);

@@ -119,25 +119,10 @@ static void sctp_enter_memory_pressure(struct sock *sk)
 /* Get the sndbuf space available at the time on the association.  */
 static inline int sctp_wspace(struct sctp_association *asoc)
 {
-	int amt;
+	struct sock *sk = asoc->base.sk;
 
-	if (asoc->ep->sndbuf_policy)
-		amt = asoc->sndbuf_used;
-	else
-		amt = sk_wmem_alloc_get(asoc->base.sk);
-
-	if (amt >= asoc->base.sk->sk_sndbuf) {
-		if (asoc->base.sk->sk_userlocks & SOCK_SNDBUF_LOCK)
-			amt = 0;
-		else {
-			amt = sk_stream_wspace(asoc->base.sk);
-			if (amt < 0)
-				amt = 0;
-		}
-	} else {
-		amt = asoc->base.sk->sk_sndbuf - amt;
-	}
-	return amt;
+	return asoc->ep->sndbuf_policy ? sk->sk_sndbuf - asoc->sndbuf_used
+				       : sk_stream_wspace(sk);
 }
 
 /* Increment the used sndbuf space count of the corresponding association by

@@ -1925,10 +1910,10 @@ static int sctp_sendmsg_to_asoc(struct sctp_association *asoc,
 		asoc->pmtu_pending = 0;
 	}
 
-	if (sctp_wspace(asoc) < msg_len)
+	if (sctp_wspace(asoc) < (int)msg_len)
 		sctp_prsctp_prune(asoc, sinfo, msg_len - sctp_wspace(asoc));
 
-	if (!sctp_wspace(asoc)) {
+	if (sctp_wspace(asoc) <= 0) {
 		timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 		err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len);
 		if (err)

@@ -8535,7 +8520,7 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
 			goto do_error;
 		if (signal_pending(current))
 			goto do_interrupted;
-		if (msg_len <= sctp_wspace(asoc))
+		if ((int)msg_len <= sctp_wspace(asoc))
 			break;
 
 		/* Let another process have a go.  Since we are going

@@ -8610,14 +8595,9 @@ void sctp_write_space(struct sock *sk)
  * UDP-style sockets or TCP-style sockets, this code should work.
  *  - Daisy
  */
-static int sctp_writeable(struct sock *sk)
+static bool sctp_writeable(struct sock *sk)
 {
-	int amt = 0;
-
-	amt = sk->sk_sndbuf - sk_wmem_alloc_get(sk);
-	if (amt < 0)
-		amt = 0;
-	return amt;
+	return sk->sk_sndbuf > sk->sk_wmem_queued;
 }
 
 /* Wait for an association to go into ESTABLISHED state. If timeout is 0,
Signature · 1 line
2.1.0
maintainer
#3 lore raw
In reply to Xin Long

From: Xin Long <[email protected]>
Date: Wed, 17 Oct 2018 03:07:49 +0800

Quoted 4 lines

sctp doesn't count and use asoc sndbuf_used, sk sk_wmem_alloc and sk_wmem_queued properly, which also causes some problem.

This patchset is to improve it.

Series applied, thanks.