[PATCH net-next v2 05/13] net: mana: swap queue sets in mana_change_mtu
From: Long Li
Date: Tue Aug 11 2026 - 02:44:32 EST
The RX buffer layout depends on the MTU - see mana_get_rxbuf_cfg() - so
changing it rebuilds the queues. Convert mana_change_mtu() to the
pre-allocate and swap helpers.
The MTU becomes part of the queue-set configuration:
- struct mana_qset gains mtu, so it is swapped atomically with the
queues it describes and restored by the rollback path.
- mana_port_context gains configured_mtu, the MTU the current RX queues
were built for. mana_create_rxq() now sizes buffers from it rather
than ndev->mtu, so a new set can be built for a different MTU while
ndev->mtu still advertises the old one.
- mana_publish_qset() commits ndev->mtu once the new set is serving
traffic. It is a no-op for callers that do not change the MTU.
Previously ndev->mtu was written before mana_attach() and rolled back on
failure, so a failed change was briefly visible to the stack.
mana_pre_alloc_rxbufs() is no longer needed here; de-risking allocation
after teardown is pointless when there is no teardown.
Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
---
drivers/net/ethernet/microsoft/mana/mana_en.c | 75 ++++++++++++++-----
.../ethernet/microsoft/mana/mana_ethtool.c | 8 +-
include/net/mana/mana.h | 14 +++-
3 files changed, 74 insertions(+), 23 deletions(-)
diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 5f682e3d5a706149954764d083b70f25906f28df..4c79d6e82d9a93786ea877fbcef2b3f9d4093a6c 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -889,35 +889,54 @@ int mana_pre_alloc_rxbufs(struct mana_port_context *mpc, int new_mtu, int num_qu
return -ENOMEM;
}
+/* mana_change_mtu - resize RX buffers for a new MTU
+ *
+ * Uses the pre-allocate + swap path: the new queue set is built for
+ * @new_mtu while the current one keeps serving traffic at the old MTU.
+ * ndev->mtu is only updated once the new set is live (see
+ * mana_publish_qset), so a failed allocation leaves both the queues and
+ * the advertised MTU untouched.
+ */
static int mana_change_mtu(struct net_device *ndev, int new_mtu)
{
struct mana_port_context *mpc = netdev_priv(ndev);
- unsigned int old_mtu = ndev->mtu;
+ struct mana_port_context *scratch;
+ struct mana_qset newq, oldq;
int err;
- /* Pre-allocate buffers to prevent failure in mana_attach later */
- err = mana_pre_alloc_rxbufs(mpc, new_mtu, mpc->num_queues);
- if (err) {
- netdev_err(ndev, "Insufficient memory for new MTU\n");
- return err;
+ /* Port is down: no queues to rebuild, just record the new MTU.
+ * mana_open() will size the RX buffers accordingly.
+ */
+ if (!mpc->port_is_up) {
+ mpc->configured_mtu = new_mtu;
+ WRITE_ONCE(ndev->mtu, new_mtu);
+ return 0;
}
- err = mana_detach(ndev, false);
- if (err) {
- netdev_err(ndev, "mana_detach failed: %d\n", err);
- goto out;
- }
+ scratch = mana_qset_scratch_alloc(mpc);
+ if (!scratch)
+ return -ENOMEM;
- WRITE_ONCE(ndev->mtu, new_mtu);
+ err = mana_alloc_qset(scratch, mpc->num_queues, mpc->rx_queue_size,
+ mpc->tx_queue_size, mpc->priv_flags, new_mtu,
+ &newq);
+ if (err)
+ goto free_scratch; /* current qset and ndev->mtu untouched */
- err = mana_attach(ndev);
+ err = mana_publish_qset(mpc, &newq, &oldq);
if (err) {
- netdev_err(ndev, "mana_attach failed: %d\n", err);
- WRITE_ONCE(ndev->mtu, old_mtu);
+ mana_free_qset(scratch, &newq);
+ goto free_scratch;
}
-out:
- mana_pre_dealloc_rxbufs(mpc);
+ mana_free_qset(scratch, &oldq);
+
+free_scratch:
+ /* After the caller-side cleanup above, so the EQ pool outlives the
+ * CQs that reference it.
+ */
+ mana_publish_close_if_needed(mpc);
+ mana_qset_scratch_free(scratch);
return err;
}
@@ -3097,7 +3116,8 @@ static struct mana_rxq *mana_create_rxq(struct mana_port_context *apc,
rxq->rxq_idx = rxq_idx;
rxq->rxobj = INVALID_MANA_HANDLE;
- mana_get_rxbuf_cfg(apc, ndev->mtu, &rxq->datasize, &rxq->alloc_size,
+ mana_get_rxbuf_cfg(apc, apc->configured_mtu, &rxq->datasize,
+ &rxq->alloc_size,
&rxq->headroom, &rxq->frag_count);
/* Create page pool for RX queue */
err = mana_create_page_pool(rxq, gc);
@@ -3965,6 +3985,7 @@ static void mana_qset_snapshot(const struct mana_port_context *ctx,
out->rx_queue_size = ctx->rx_queue_size;
out->tx_queue_size = ctx->tx_queue_size;
out->priv_flags = ctx->priv_flags;
+ out->mtu = ctx->configured_mtu;
out->mana_eqs_debugfs = ctx->mana_eqs_debugfs;
}
@@ -3986,6 +4007,7 @@ static void mana_qset_install(struct mana_port_context *ctx,
ctx->rx_queue_size = qset->rx_queue_size;
ctx->tx_queue_size = qset->tx_queue_size;
ctx->priv_flags = qset->priv_flags;
+ ctx->configured_mtu = qset->mtu;
ctx->mana_eqs_debugfs = qset->mana_eqs_debugfs;
}
@@ -4049,6 +4071,7 @@ void mana_qset_scratch_free(struct mana_port_context *scratch)
* @rx_queue_size: new RX ring size
* @tx_queue_size: new TX ring size
* @priv_flags: new priv-flag word (affects full-page RX)
+ * @mtu: MTU the new set is sized for
* @out: output qset, populated on success
*
* The live port context is not referenced at all, so the currently
@@ -4057,7 +4080,7 @@ void mana_qset_scratch_free(struct mana_port_context *scratch)
*/
int mana_alloc_qset(struct mana_port_context *scratch, unsigned int num_queues,
unsigned int rx_queue_size, unsigned int tx_queue_size,
- u32 priv_flags, struct mana_qset *out)
+ u32 priv_flags, int mtu, struct mana_qset *out)
{
struct net_device *ndev = scratch->ndev;
int err;
@@ -4069,6 +4092,12 @@ int mana_alloc_qset(struct mana_port_context *scratch, unsigned int num_queues,
scratch->tx_queue_size = tx_queue_size;
scratch->priv_flags = priv_flags;
+ /* mana_get_rxbuf_cfg() reads this when sizing RX buffers, so the
+ * new set is built for the requested MTU without disturbing the
+ * running set.
+ */
+ scratch->configured_mtu = mtu;
+
err = mana_init_port_context(scratch);
if (err)
goto out_err;
@@ -4361,6 +4390,11 @@ int mana_publish_qset(struct mana_port_context *apc, struct mana_qset *newq,
if (err)
goto rollback;
+ /* The new set is serving traffic: advertise its MTU. A no-op for
+ * callers that are not changing the MTU.
+ */
+ WRITE_ONCE(ndev->mtu, apc->configured_mtu);
+
/* Pair with the queue-state stores above: a datapath reader that sees
* the gate open must also see the queue set it is about to index.
*/
@@ -4413,6 +4447,8 @@ int mana_publish_qset(struct mana_port_context *apc, struct mana_qset *newq,
return err;
}
+ WRITE_ONCE(ndev->mtu, apc->configured_mtu);
+
/* Same pairing as the success path: the restored queue set has to be
* visible before the gate reopens on it.
*/
@@ -4658,6 +4694,7 @@ static int mana_probe_port(struct mana_context *ac, int port_idx,
apc->port_handle = INVALID_MANA_HANDLE;
apc->pf_filter_handle = INVALID_MANA_HANDLE;
apc->port_idx = port_idx;
+ apc->configured_mtu = ndev->mtu;
apc->link_cfg_error = 1;
apc->cqe_coalescing_enable = 0;
apc->cqe8_coalescing_enable = 0;
diff --git a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
index 9392b82d3d48a2638512a53f9c004629b0c679e5..2a6325256fad3edf1aafbc72f0cd5dc18d61384e 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
@@ -737,7 +737,8 @@ static int mana_set_channels(struct net_device *ndev,
}
err = mana_alloc_qset(scratch, new_count, apc->rx_queue_size,
- apc->tx_queue_size, apc->priv_flags, &newq);
+ apc->tx_queue_size, apc->priv_flags,
+ apc->configured_mtu, &newq);
if (err)
goto free_scratch; /* current qset untouched, nothing to undo */
@@ -839,7 +840,7 @@ static int mana_set_ringparam(struct net_device *ndev,
}
err = mana_alloc_qset(scratch, apc->num_queues, new_rx, new_tx,
- apc->priv_flags, &newq);
+ apc->priv_flags, apc->configured_mtu, &newq);
if (err) {
NL_SET_ERR_MSG_FMT(extack, "failed to change ring params: %d",
err);
@@ -940,7 +941,8 @@ static int mana_set_priv_flags(struct net_device *ndev, u32 priv_flags)
}
err = mana_alloc_qset(scratch, apc->num_queues, apc->rx_queue_size,
- apc->tx_queue_size, priv_flags, &newq);
+ apc->tx_queue_size, priv_flags,
+ apc->configured_mtu, &newq);
if (err)
goto free_scratch; /* current qset and priv_flags untouched */
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index e4aaad7bec34297cf406181560a1839d3e6a73df..2fc75e6cd41a63878788182cd099379c8c698b33 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -621,6 +621,12 @@ struct mana_port_context {
unsigned int rx_queue_size;
unsigned int tx_queue_size;
+ /* MTU the current RX queues were built for. Normally equal to
+ * ndev->mtu, but during a queue-set swap the new set is built for
+ * the new MTU while ndev->mtu still advertises the old one.
+ */
+ int configured_mtu;
+
mana_handle_t port_handle;
mana_handle_t pf_filter_handle;
@@ -714,6 +720,12 @@ struct mana_qset {
unsigned int tx_queue_size;
u32 priv_flags;
+ /* MTU the RX buffers of this set were sized for. It feeds
+ * mana_get_rxbuf_cfg(), so it is part of the queue-set
+ * configuration and must be swapped atomically with the queues.
+ */
+ int mtu;
+
/* Per-queue-set debugfs root ("EQs"). Owned by the qset: it is
* recreated by mana_create_eq() for each new set and torn down
* with that set, so it must travel with the qset rather than
@@ -739,7 +751,7 @@ struct mana_port_context *mana_qset_scratch_alloc(struct mana_port_context *apc)
void mana_qset_scratch_free(struct mana_port_context *scratch);
int mana_alloc_qset(struct mana_port_context *scratch, unsigned int num_queues,
unsigned int rx_queue_size, unsigned int tx_queue_size,
- u32 priv_flags, struct mana_qset *out);
+ u32 priv_flags, int mtu, struct mana_qset *out);
int mana_publish_qset(struct mana_port_context *apc, struct mana_qset *newq,
struct mana_qset *out_old);
void mana_publish_close_if_needed(struct mana_port_context *apc);
--
2.43.0