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FAILED: Patch "smb: server: fix last send credit problem causing disconnects" failed to apply to 5.10-stable tree

PATCH Sasha Levin 1 participant 1 message Mar 1

Subsystems (4)
Stable branch SMB client (CIFS) Kernel SMB3 server (ksmbd) Smbdirect (RDMA Stream Transport with Read/Write-Offload, MS-SMBD)
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Sasha Levin

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The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 8cf2bbac6281434065f5f3aeab19c9c08ff755a2 Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <[email protected]>
Date: Thu, 22 Jan 2026 18:16:46 +0100
Subject: [PATCH] smb: server: fix last send credit problem causing disconnects

When we are about to use the last send credit that was granted to us by the peer, we need to wait until we are ourself able to grant at least one credit to the peer. Otherwise it might not be possible for the peer to grant more credits.

The following sections in MS-SMBD are related to this:

3.1.5.1 Sending Upper Layer Messages
...
If Connection.SendCredits is 1 and the CreditsGranted field of the message is 0, stop processing.
...

3.1.5.9 Managing Credits Prior to Sending
...
If Connection.ReceiveCredits is zero, or if Connection.SendCredits is one and the Connection.SendQueue is not empty, the sender MUST allocate and post at least one receive of size Connection.MaxReceiveSize and MUST increment Connection.ReceiveCredits by the number allocated and posted. If no receives are posted, the processing MUST return a value of zero to indicate to the caller that no Send message can be currently performed.
...

This problem was found by running this on Windows 2025 against ksmbd with required smb signing:
'frametest.exe -r 4k -t 20 -n 2000' after 'frametest.exe -w 4k -t 20 -n 2000'.

Link https://lore.kernel.org/linux-cifs/[email protected]/ open here
Cc <[email protected]> # 6.18.x
Cc Namjae Jeon <[email protected]>
Cc Steve French <[email protected]>
Cc Tom Talpey <[email protected]>
Cc [email protected]
Cc [email protected]
Signed-off-by Stefan Metzmacher <[email protected]>
Acked-by Namjae Jeon <[email protected]>
Signed-off-by Steve French <[email protected]>
---
 fs/smb/server/transport_rdma.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)
fs/smb/server/transport_rdma.c +30 -2
index 38248b6a1b5ca..5c0cc5064e8c0 100644
@@ -1033,6 +1033,15 @@ static void smb_direct_post_recv_credits(struct work_struct *work)
 
 	atomic_add(credits, &sc->recv_io.credits.available);
 
+	/*
+	 * If the last send credit is waiting for credits
+	 * it can grant we need to wake it up
+	 */
+	if (credits &&
+	    atomic_read(&sc->send_io.bcredits.count) == 0 &&
+	    atomic_read(&sc->send_io.credits.count) == 0)
+		wake_up(&sc->send_io.credits.wait_queue);
+
 	if (credits)
 		queue_work(sc->workqueue, &sc->idle.immediate_work);
 }

@@ -1306,6 +1315,7 @@ static int calc_rw_credits(struct smbdirect_socket *sc,
 
 static int smb_direct_create_header(struct smbdirect_socket *sc,
 				    int size, int remaining_data_length,
+				    int new_credits,
 				    struct smbdirect_send_io **sendmsg_out)
 {
 	struct smbdirect_socket_parameters *sp = &sc->parameters;

@@ -1321,7 +1331,7 @@ static int smb_direct_create_header(struct smbdirect_socket *sc,
 	/* Fill in the packet header */
 	packet = (struct smbdirect_data_transfer *)sendmsg->packet;
 	packet->credits_requested = cpu_to_le16(sp->send_credit_target);
-	packet->credits_granted = cpu_to_le16(manage_credits_prior_sending(sc));
+	packet->credits_granted = cpu_to_le16(new_credits);
 
 	packet->flags = 0;
 	if (manage_keep_alive_before_sending(sc))

@@ -1459,6 +1469,7 @@ static int smb_direct_post_send_data(struct smbdirect_socket *sc,
 	int data_length;
 	struct scatterlist sg[SMBDIRECT_SEND_IO_MAX_SGE - 1];
 	struct smbdirect_send_batch _send_ctx;
+	int new_credits;
 
 	if (!send_ctx) {
 		smb_direct_send_ctx_init(&_send_ctx, false, 0);

@@ -1477,12 +1488,29 @@ static int smb_direct_post_send_data(struct smbdirect_socket *sc,
 	if (ret)
 		goto credit_failed;
 
+	new_credits = manage_credits_prior_sending(sc);
+	if (new_credits == 0 &&
+	    atomic_read(&sc->send_io.credits.count) == 0 &&
+	    atomic_read(&sc->recv_io.credits.count) == 0) {
+		queue_work(sc->workqueue, &sc->recv_io.posted.refill_work);
+		ret = wait_event_interruptible(sc->send_io.credits.wait_queue,
+					       atomic_read(&sc->send_io.credits.count) >= 1 ||
+					       atomic_read(&sc->recv_io.credits.available) >= 1 ||
+					       sc->status != SMBDIRECT_SOCKET_CONNECTED);
+		if (sc->status != SMBDIRECT_SOCKET_CONNECTED)
+			ret = -ENOTCONN;
+		if (ret < 0)
+			goto credit_failed;
+
+		new_credits = manage_credits_prior_sending(sc);
+	}
+
 	data_length = 0;
 	for (i = 0; i < niov; i++)
 		data_length += iov[i].iov_len;
 
 	ret = smb_direct_create_header(sc, data_length, remaining_data_length,
-				       &msg);
+				       new_credits, &msg);
 	if (ret)
 		goto header_failed;
Signature · 1 line
2.51.0