On Fri, Jul 31, 2026 at 06:23:22PM +0200, Laurent Vivier wrote:
Static buffers shared across all call sites are not safe when multiple worker threads handle TCP connections concurrently.
In tcp.c, move tcp_iov[] from file scope into tcp_data_from_tap() where it is exclusively used. At UIO_MAXIOV (1024) entries of struct iovec (16 bytes each), this adds 16 KiB to the stack frame.
In tcp_vu.c, move iov_vu[], elem[], and frame[] from file scope into tcp_vu_data_from_sock() and pass them to tcp_vu_sock_recv() as parameters. Also make iov_msg[] in tcp_vu_sock_recv() a local variable instead of static, as it is only used within a single call. Combined, these add roughly 80 KiB across the nested stack frames, which is acceptable for per-thread stacks.
Signed-off-by: Laurent Vivier
Reviewed-by: David Gibson
--- tcp.c | 3 +-- tcp_vu.c | 33 ++++++++++++++++++++------------- 2 files changed, 21 insertions(+), 15 deletions(-)
diff --git a/tcp.c b/tcp.c index e80a64e38f24..ee4ec599e055 100644 --- a/tcp.c +++ b/tcp.c @@ -435,8 +435,6 @@ static socklen_t tcp_info_size; /* Kernel reports delivery rate in TCP_INFO (kernel commit eb8329e0a04d) */ #define delivery_rate_cap tcp_info_cap(delivery_rate)
-/* sendmsg() to socket */ -static struct iovec tcp_iov [UIO_MAXIOV];
/* Pools for pre-opened sockets (in init) */ int init_sock_pool4 [TCP_SOCK_POOL_SIZE]; @@ -1945,6 +1943,7 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn, uint16_t max_ack_seq_wnd = conn->wnd_from_tap; uint32_t max_ack_seq = conn->seq_ack_from_tap; uint32_t seq_from_tap = conn->seq_from_tap; + struct iovec tcp_iov[UIO_MAXIOV]; struct msghdr mh = { .msg_iov = tcp_iov }; size_t len; ssize_t n; diff --git a/tcp_vu.c b/tcp_vu.c index c9a1e08747b5..b4baecc1f717 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -35,9 +35,6 @@ #include "vu_common.h" #include
-static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE]; -static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; - /** * struct vu_frame - Descriptor for a TCP frame mapped to virtqueue elements * @idx_element: Index of first element in elem[] for this frame @@ -46,13 +43,13 @@ static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; * @num_iovec: Number of iovecs covering this frame's buffers * @size: Total frame size including all headers */ -static struct vu_frame { +struct vu_frame { int idx_element; int num_element; int idx_iovec; int num_iovec; size_t size; -} frame[VIRTQUEUE_MAX_SIZE]; +};
/** * tcp_vu_hdrlen() - Sum size of all headers, from TCP to virtio-net @@ -225,6 +222,9 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags, * @v6: Set for IPv6 connections * @already_sent: Number of bytes already sent * @fillsize: Maximum bytes to fill in guest-side receiving window + * @iov_vu: IO vector array for virtqueue buffers + * @elem: Virtqueue element array + * @frame: Frame descriptor array * @elem_used: number of element (output) * @frame_cnt: Pointer to store the number of frames (output) * @@ -234,9 +234,12 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags, static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, const struct tcp_tap_conn *conn, bool v6, uint32_t already_sent, size_t fillsize, + struct iovec *iov_vu, + struct vu_virtq_element *elem, + struct vu_frame *frame, int *elem_used, int *frame_cnt) { - static struct iovec iov_msg[VIRTQUEUE_MAX_SIZE + DISCARD_IOV_NUM]; + struct iovec iov_msg[VIRTQUEUE_MAX_SIZE + DISCARD_IOV_NUM]; const struct vu_dev *vdev = c->vdev; struct msghdr mh_sock = { 0 }; uint16_t mss = MSS_GET(conn); @@ -253,16 +256,16 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, iov_used = 0; elem_cnt = 0; *frame_cnt = 0; - while (fillsize > 0 && elem_cnt < ARRAY_SIZE(elem) && - iov_used < ARRAY_SIZE(iov_vu) && - *frame_cnt < ARRAY_SIZE(frame)) { + while (fillsize > 0 && elem_cnt < VIRTQUEUE_MAX_SIZE && + iov_used < VIRTQUEUE_MAX_SIZE && + *frame_cnt < VIRTQUEUE_MAX_SIZE) { size_t frame_size, in_total; int cnt;
cnt = vu_collect(vdev, vq, &elem[elem_cnt], - ARRAY_SIZE(elem) - elem_cnt, + VIRTQUEUE_MAX_SIZE - elem_cnt, &iov_vu[iov_used], - ARRAY_SIZE(iov_vu) - iov_used, &in_total, + VIRTQUEUE_MAX_SIZE - iov_used, &in_total, MIN(mss, fillsize) + hdrlen, &frame_size); if (cnt == 0) @@ -328,7 +331,8 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, if ((size_t)ret <= f->size - hdrlen) { unsigned cnt;
- cnt = iov_skip_bytes(&iov_vu[f->idx_iovec], f->num_iovec, + cnt = iov_skip_bytes(&iov_vu[f->idx_iovec], + f->num_iovec, MAX(hdrlen + ret, VNET_HLEN + ETH_ZLEN), NULL); if (cnt < (unsigned)f->num_iovec) @@ -437,6 +441,9 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn, uint32_t already_sent, const struct timespec *now, unsigned int qpair) { + struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; + struct iovec iov_vu[VIRTQUEUE_MAX_SIZE]; + struct vu_frame frame[VIRTQUEUE_MAX_SIZE]; uint32_t wnd_scaled = conn->wnd_from_tap << conn->ws_from_tap; int toguest = QPAIR_TOGUEST_QUEUE(qpair); struct vu_dev *vdev = c->vdev; @@ -460,7 +467,7 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn, * data from the socket */ len = tcp_vu_sock_recv(c, vq, conn, v6, already_sent, fillsize, - &elem_cnt, &frame_cnt); + iov_vu, elem, frame, &elem_cnt, &frame_cnt); if (len < 0) { if (len != -EAGAIN && len != -EWOULDBLOCK) { tcp_rst(c, conn, now, qpair); -- 2.54.0
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson