[SRU][J:linux-azure][PATCH 1/2] net: mana: Improve mana_set_channels() in low mem conditions

[John Cabaj]

From: Shradha Gupta <shradhagupta at linux.microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/2121570

The mana_set_channels() function requires detaching the mana
driver and reattaching it with changed channel values.
During this operation if the system is low on memory, the reattach
might fail, causing the network device being down.
To avoid this we pre-allocate buffers at the beginning of set operation,
to prevent complete network loss

Signed-off-by: Shradha Gupta <shradhagupta at linux.microsoft.com>
Reviewed-by: Gerhard Engleder <gerhard at engleder-embedded.com>
Reviewed-by: Haiyang Zhang <haiyangz at microsoft.com>
Link: https://patch.msgid.link/1725248734-21760-1-git-send-email-shradhagupta@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(backported from commit 1705341485ff1eec097dfa26891d03afe5907e16)
[john-cabaj: context changes]
Signed-off-by: John Cabaj <john.cabaj at canonical.com>
---
 drivers/net/ethernet/microsoft/mana/mana_en.c |  6 ++--
 .../ethernet/microsoft/mana/mana_ethtool.c    | 28 ++++++++++---------
 include/net/mana/mana.h                       |  2 +-
 3 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 87eff5062c8f..945c5871025f 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -631,7 +631,7 @@ static void mana_get_rxbuf_cfg(int mtu, u32 *datasize, u32 *alloc_size,
 	*datasize = mtu + ETH_HLEN;
 }
 
-int mana_pre_alloc_rxbufs(struct mana_port_context *mpc, int new_mtu)
+int mana_pre_alloc_rxbufs(struct mana_port_context *mpc, int new_mtu, int num_queues)
 {
 	struct device *dev;
 	struct page *page;
@@ -645,7 +645,7 @@ int mana_pre_alloc_rxbufs(struct mana_port_context *mpc, int new_mtu)
 
 	dev = mpc->ac->gdma_dev->gdma_context->dev;
 
-	num_rxb = mpc->num_queues * mpc->rx_queue_size;
+	num_rxb = num_queues * mpc->rx_queue_size;
 
 	WARN(mpc->rxbufs_pre, "mana rxbufs_pre exists\n");
 	mpc->rxbufs_pre = kmalloc_array(num_rxb, sizeof(void *), GFP_KERNEL);
@@ -692,7 +692,7 @@ static int mana_change_mtu(struct net_device *ndev, int new_mtu)
 	int err;
 
 	/* Pre-allocate buffers to prevent failure in mana_attach later */
-	err = mana_pre_alloc_rxbufs(mpc, new_mtu);
+	err = mana_pre_alloc_rxbufs(mpc, new_mtu, mpc->num_queues);
 	if (err) {
 		netdev_err(ndev, "Insufficient memory for new MTU\n");
 		return err;
diff --git a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
index a7d5bd81f18c..c583f8800e43 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_ethtool.c
@@ -349,27 +349,29 @@ static int mana_set_channels(struct net_device *ndev,
 	struct mana_port_context *apc = netdev_priv(ndev);
 	unsigned int new_count = channels->combined_count;
 	unsigned int old_count = apc->num_queues;
-	int err, err2;
+	int err;
+
+	err = mana_pre_alloc_rxbufs(apc, ndev->mtu, new_count);
+	if (err) {
+		netdev_err(ndev, "Insufficient memory for new allocations");
+		return err;
+	}
 
 	err = mana_detach(ndev, false);
 	if (err) {
 		netdev_err(ndev, "mana_detach failed: %d\n", err);
-		return err;
+		goto out;
 	}
 
 	apc->num_queues = new_count;
 	err = mana_attach(ndev);
-	if (!err)
-		return 0;
-
-	netdev_err(ndev, "mana_attach failed: %d\n", err);
-
-	/* Try to roll it back to the old configuration. */
-	apc->num_queues = old_count;
-	err2 = mana_attach(ndev);
-	if (err2)
-		netdev_err(ndev, "mana re-attach failed: %d\n", err2);
+	if (err) {
+		apc->num_queues = old_count;
+		netdev_err(ndev, "mana_attach failed: %d\n", err);
+	}
 
+out:
+	mana_pre_dealloc_rxbufs(apc);
 	return err;
 }
 
@@ -414,7 +416,7 @@ static int mana_set_ringparam(struct net_device *ndev,
 
 	/* pre-allocating new buffers to prevent failures in mana_attach() later */
 	apc->rx_queue_size = new_rx;
-	err = mana_pre_alloc_rxbufs(apc, ndev->mtu);
+	err = mana_pre_alloc_rxbufs(apc, ndev->mtu, apc->num_queues);
 	apc->rx_queue_size = old_rx;
 	if (err) {
 		netdev_err(ndev, "Insufficient memory for new allocations\n");
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index 4d6d6699a906..e81e259cf5cf 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -536,7 +536,7 @@ u32 mana_run_xdp(struct net_device *ndev, struct mana_rxq *rxq,
 struct bpf_prog *mana_xdp_get(struct mana_port_context *apc);
 void mana_chn_setxdp(struct mana_port_context *apc, struct bpf_prog *prog);
 int mana_bpf(struct net_device *ndev, struct netdev_bpf *bpf);
-int mana_pre_alloc_rxbufs(struct mana_port_context *apc, int mtu);
+int mana_pre_alloc_rxbufs(struct mana_port_context *apc, int mtu, int num_queues);
 void mana_query_phy_stats(struct mana_port_context *apc);
 void mana_pre_dealloc_rxbufs(struct mana_port_context *apc);
 void mana_query_gf_stats(struct mana_port_context *apc);
-- 
2.43.0