[PATCH AUTOSEL 4.19 079/237] sctp: use sk_wmem_queued to check for writable space

Sasha Levin
2019-11-16T16:23:29Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit cd305c74b0f8b49748a79a8f67fc8e5e3e0c4794 ]

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 <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/socket.c | 38 +++++++++-----------------------------
1 file changed, 9 insertions(+), 29 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c766315527226..e7a11cd7633f5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -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
@@ -1928,10 +1913,10 @@ 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)
@@ -8516,7 +8501,7 @@ 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
@@ -8591,14 +8576,9 @@ 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,
--
2.20.1