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mptcp: move the whole rx path under msk socket lock protection
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After commit c2e6048 ("mptcp: fix race in release_cb") we can
move the whole MPTCP rx path under the socket lock leveraging the
release_cb.

We can drop a bunch of spin_lock pairs in the receive functions, use
a single receive queue and invoke __mptcp_move_skbs only when subflows
ask for it.

This will allow more cleanup in the next patch.

Some changes are worth specific mention:

The msk rcvbuf update now always happens under both the msk and the
subflow socket lock: we can drop a bunch of ONCE annotation and
consolidate the checks.

When the skbs move is delayed at msk release callback time, even the
msk rcvbuf update is delayed; additionally take care of such action in
__mptcp_move_skbs().

Signed-off-by: Paolo Abeni <[email protected]>
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@intel-lab-lkp
Paolo Abeni authored and intel-lab-lkp committed Dec 6, 2024
1 parent 420b898 commit edf6b4b
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Showing 3 changed files with 61 additions and 66 deletions.
2 changes: 2 additions & 0 deletions net/mptcp/fastopen.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
MPTCP_SKB_CB(skb)->has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;

mptcp_data_lock(sk);
DEBUG_NET_WARN_ON_ONCE(sock_owned_by_user_nocheck(sk));

mptcp_set_owner_r(skb, sk);
__skb_queue_tail(&sk->sk_receive_queue, skb);
Expand All @@ -65,6 +66,7 @@ void __mptcp_fastopen_gen_msk_ackseq(struct mptcp_sock *msk, struct mptcp_subflo
struct sock *sk = (struct sock *)msk;
struct sk_buff *skb;

DEBUG_NET_WARN_ON_ONCE(sock_owned_by_user_nocheck(sk));
skb = skb_peek_tail(&sk->sk_receive_queue);
if (skb) {
WARN_ON_ONCE(MPTCP_SKB_CB(skb)->end_seq);
Expand Down
123 changes: 58 additions & 65 deletions net/mptcp/protocol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -643,18 +643,6 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
bool more_data_avail;
struct tcp_sock *tp;
bool done = false;
int sk_rbuf;

sk_rbuf = READ_ONCE(sk->sk_rcvbuf);

if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
int ssk_rbuf = READ_ONCE(ssk->sk_rcvbuf);

if (unlikely(ssk_rbuf > sk_rbuf)) {
WRITE_ONCE(sk->sk_rcvbuf, ssk_rbuf);
sk_rbuf = ssk_rbuf;
}
}

pr_debug("msk=%p ssk=%p\n", msk, ssk);
tp = tcp_sk(ssk);
Expand Down Expand Up @@ -722,7 +710,7 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
WRITE_ONCE(tp->copied_seq, seq);
more_data_avail = mptcp_subflow_data_available(ssk);

if (atomic_read(&sk->sk_rmem_alloc) > sk_rbuf) {
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) {
done = true;
break;
}
Expand Down Expand Up @@ -846,11 +834,30 @@ static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
return moved > 0;
}

static void __mptcp_rcvbuf_update(struct sock *sk, struct sock *ssk)
{
if (unlikely(ssk->sk_rcvbuf > sk->sk_rcvbuf))
WRITE_ONCE(sk->sk_rcvbuf, ssk->sk_rcvbuf);
}

static void __mptcp_data_ready(struct sock *sk, struct sock *ssk)
{
struct mptcp_sock *msk = mptcp_sk(sk);

__mptcp_rcvbuf_update(sk, ssk);

/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
if (__mptcp_rmem(sk) > sk->sk_rcvbuf)
return;

/* Wake-up the reader only for in-sequence data */
if (move_skbs_to_msk(msk, ssk) && mptcp_epollin_ready(sk))
sk->sk_data_ready(sk);
}

void mptcp_data_ready(struct sock *sk, struct sock *ssk)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
struct mptcp_sock *msk = mptcp_sk(sk);
int sk_rbuf, ssk_rbuf;

/* The peer can send data while we are shutting down this
* subflow at msk destruction time, but we must avoid enqueuing
Expand All @@ -859,19 +866,11 @@ void mptcp_data_ready(struct sock *sk, struct sock *ssk)
if (unlikely(subflow->disposable))
return;

ssk_rbuf = READ_ONCE(ssk->sk_rcvbuf);
sk_rbuf = READ_ONCE(sk->sk_rcvbuf);
if (unlikely(ssk_rbuf > sk_rbuf))
sk_rbuf = ssk_rbuf;

/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
if (__mptcp_rmem(sk) > sk_rbuf)
return;

/* Wake-up the reader only for in-sequence data */
mptcp_data_lock(sk);
if (move_skbs_to_msk(msk, ssk) && mptcp_epollin_ready(sk))
sk->sk_data_ready(sk);
if (!sock_owned_by_user(sk))
__mptcp_data_ready(sk, ssk);
else
__set_bit(MPTCP_DEQUEUE, &mptcp_sk(sk)->cb_flags);
mptcp_data_unlock(sk);
}

Expand Down Expand Up @@ -1942,16 +1941,17 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)

static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied);

static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
static int __mptcp_recvmsg_mskq(struct sock *sk,
struct msghdr *msg,
size_t len, int flags,
struct scm_timestamping_internal *tss,
int *cmsg_flags)
{
struct mptcp_sock *msk = mptcp_sk(sk);
struct sk_buff *skb, *tmp;
int copied = 0;

skb_queue_walk_safe(&msk->receive_queue, skb, tmp) {
skb_queue_walk_safe(&sk->sk_receive_queue, skb, tmp) {
u32 offset = MPTCP_SKB_CB(skb)->offset;
u32 data_len = skb->len - offset;
u32 count = min_t(size_t, len - copied, data_len);
Expand Down Expand Up @@ -1986,7 +1986,7 @@ static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
/* we will bulk release the skb memory later */
skb->destructor = NULL;
WRITE_ONCE(msk->rmem_released, msk->rmem_released + skb->truesize);
__skb_unlink(skb, &msk->receive_queue);
__skb_unlink(skb, &sk->sk_receive_queue);
__kfree_skb(skb);
msk->bytes_consumed += count;
}
Expand Down Expand Up @@ -2111,62 +2111,54 @@ static void __mptcp_update_rmem(struct sock *sk)
WRITE_ONCE(msk->rmem_released, 0);
}

static void __mptcp_splice_receive_queue(struct sock *sk)
static bool __mptcp_move_skbs(struct sock *sk)
{
struct mptcp_subflow_context *subflow;
struct mptcp_sock *msk = mptcp_sk(sk);

skb_queue_splice_tail_init(&sk->sk_receive_queue, &msk->receive_queue);
}

static bool __mptcp_move_skbs(struct mptcp_sock *msk)
{
struct sock *sk = (struct sock *)msk;
unsigned int moved = 0;
bool ret, done;

/* verify we can move any data from the subflow, eventually updating */
if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
mptcp_for_each_subflow(msk, subflow)
__mptcp_rcvbuf_update(sk, subflow->tcp_sock);

if (__mptcp_rmem(sk) > sk->sk_rcvbuf)
return false;

do {
struct sock *ssk = mptcp_subflow_recv_lookup(msk);
bool slowpath;

/* we can have data pending in the subflows only if the msk
* receive buffer was full at subflow_data_ready() time,
* that is an unlikely slow path.
*/
if (likely(!ssk))
if (unlikely(!ssk))
break;

slowpath = lock_sock_fast(ssk);
mptcp_data_lock(sk);
__mptcp_update_rmem(sk);
done = __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
mptcp_data_unlock(sk);

if (unlikely(ssk->sk_err))
__mptcp_error_report(sk);
unlock_sock_fast(ssk, slowpath);
} while (!done);

/* acquire the data lock only if some input data is pending */
ret = moved > 0;
if (!RB_EMPTY_ROOT(&msk->out_of_order_queue) ||
!skb_queue_empty_lockless(&sk->sk_receive_queue)) {
mptcp_data_lock(sk);
!skb_queue_empty(&sk->sk_receive_queue)) {
__mptcp_update_rmem(sk);
ret |= __mptcp_ofo_queue(msk);
__mptcp_splice_receive_queue(sk);
mptcp_data_unlock(sk);
}
if (ret)
mptcp_check_data_fin((struct sock *)msk);
return !skb_queue_empty(&msk->receive_queue);
return ret;
}

static unsigned int mptcp_inq_hint(const struct sock *sk)
{
const struct mptcp_sock *msk = mptcp_sk(sk);
const struct sk_buff *skb;

skb = skb_peek(&msk->receive_queue);
skb = skb_peek(&sk->sk_receive_queue);
if (skb) {
u64 hint_val = READ_ONCE(msk->ack_seq) - MPTCP_SKB_CB(skb)->map_seq;

Expand Down Expand Up @@ -2212,7 +2204,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
while (copied < len) {
int err, bytes_read;

bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied, flags, &tss, &cmsg_flags);
bytes_read = __mptcp_recvmsg_mskq(sk, msg, len - copied, flags, &tss, &cmsg_flags);
if (unlikely(bytes_read < 0)) {
if (!copied)
copied = bytes_read;
Expand All @@ -2221,7 +2213,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,

copied += bytes_read;

if (skb_queue_empty(&msk->receive_queue) && __mptcp_move_skbs(msk))
if (skb_queue_empty(&sk->sk_receive_queue) && __mptcp_move_skbs(sk))
continue;

/* only the MPTCP socket status is relevant here. The exit
Expand All @@ -2247,7 +2239,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
/* race breaker: the shutdown could be after the
* previous receive queue check
*/
if (__mptcp_move_skbs(msk))
if (__mptcp_move_skbs(sk))
continue;
break;
}
Expand Down Expand Up @@ -2291,9 +2283,8 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
}
}

pr_debug("msk=%p rx queue empty=%d:%d copied=%d\n",
msk, skb_queue_empty_lockless(&sk->sk_receive_queue),
skb_queue_empty(&msk->receive_queue), copied);
pr_debug("msk=%p rx queue empty=%d copied=%d\n",
msk, skb_queue_empty(&sk->sk_receive_queue), copied);

release_sock(sk);
return copied;
Expand Down Expand Up @@ -2820,7 +2811,6 @@ static void __mptcp_init_sock(struct sock *sk)
INIT_LIST_HEAD(&msk->join_list);
INIT_LIST_HEAD(&msk->rtx_queue);
INIT_WORK(&msk->work, mptcp_worker);
__skb_queue_head_init(&msk->receive_queue);
msk->out_of_order_queue = RB_ROOT;
msk->first_pending = NULL;
WRITE_ONCE(msk->rmem_fwd_alloc, 0);
Expand Down Expand Up @@ -3403,12 +3393,8 @@ void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags)
mptcp_for_each_subflow_safe(msk, subflow, tmp)
__mptcp_close_ssk(sk, mptcp_subflow_tcp_sock(subflow), subflow, flags);

/* move to sk_receive_queue, sk_stream_kill_queues will purge it */
mptcp_data_lock(sk);
skb_queue_splice_tail_init(&msk->receive_queue, &sk->sk_receive_queue);
__skb_queue_purge(&sk->sk_receive_queue);
skb_rbtree_purge(&msk->out_of_order_queue);
mptcp_data_unlock(sk);

/* move all the rx fwd alloc into the sk_mem_reclaim_final in
* inet_sock_destruct() will dispose it
Expand Down Expand Up @@ -3451,7 +3437,8 @@ void __mptcp_check_push(struct sock *sk, struct sock *ssk)

#define MPTCP_FLAGS_PROCESS_CTX_NEED (BIT(MPTCP_PUSH_PENDING) | \
BIT(MPTCP_RETRANSMIT) | \
BIT(MPTCP_FLUSH_JOIN_LIST))
BIT(MPTCP_FLUSH_JOIN_LIST) | \
BIT(MPTCP_DEQUEUE))

/* processes deferred events and flush wmem */
static void mptcp_release_cb(struct sock *sk)
Expand Down Expand Up @@ -3485,6 +3472,11 @@ static void mptcp_release_cb(struct sock *sk)
__mptcp_push_pending(sk, 0);
if (flags & BIT(MPTCP_RETRANSMIT))
__mptcp_retrans(sk);
if ((flags & BIT(MPTCP_DEQUEUE)) && __mptcp_move_skbs(sk)) {
/* notify ack seq update */
mptcp_cleanup_rbuf(msk, 0);
sk->sk_data_ready(sk);
}

cond_resched();
spin_lock_bh(&sk->sk_lock.slock);
Expand Down Expand Up @@ -3722,7 +3714,8 @@ static int mptcp_ioctl(struct sock *sk, int cmd, int *karg)
return -EINVAL;

lock_sock(sk);
__mptcp_move_skbs(msk);
if (__mptcp_move_skbs(sk))
mptcp_cleanup_rbuf(msk, 0);
*karg = mptcp_inq_hint(sk);
release_sock(sk);
break;
Expand Down
2 changes: 1 addition & 1 deletion net/mptcp/protocol.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,7 @@
#define MPTCP_FLUSH_JOIN_LIST 5
#define MPTCP_SYNC_STATE 6
#define MPTCP_SYNC_SNDBUF 7
#define MPTCP_DEQUEUE 8

struct mptcp_skb_cb {
u64 map_seq;
Expand Down Expand Up @@ -322,7 +323,6 @@ struct mptcp_sock {
struct work_struct work;
struct sk_buff *ooo_last_skb;
struct rb_root out_of_order_queue;
struct sk_buff_head receive_queue;
struct list_head conn_list;
struct list_head rtx_queue;
struct mptcp_data_frag *first_pending;
Expand Down

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