FAILED: Patch "smb: client: make use of smbdirect_socket.send_io.bcredits" failed to apply to 5.15-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

Thanks,
Sasha

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

From 21538121efe6c8c5b51c742fa02cbe820bc48714 Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <metze@samba.org>
Date: Thu, 22 Jan 2026 18:16:57 +0100
Subject: [PATCH] smb: client: make use of smbdirect_socket.send_io.bcredits

It turns out that our code will corrupt the stream of
reassabled data transfer messages when we trigger an
immendiate (empty) send.

In order to fix this we'll have a single 'batch' credit per
connection. And code getting that credit is free to use
as much messages until remaining_length reaches 0, then
the batch credit it given back and the next logical send can
happen.

Cc: <stable@vger.kernel.org> # 6.18.x
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/smb/client/smbdirect.c | 58 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index ef3b237bccc13..dbb2d939bc44d 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -657,6 +657,7 @@ static bool process_negotiation_response(
 			sp->max_frmr_depth * PAGE_SIZE);
 	sp->max_frmr_depth = sp->max_read_write_size / PAGE_SIZE;
 
+	atomic_set(&sc->send_io.bcredits.count, 1);
 	sc->recv_io.expected = SMBDIRECT_EXPECT_DATA_TRANSFER;
 	return true;
 }
@@ -1214,6 +1215,7 @@ static void smbd_send_batch_init(struct smbdirect_send_batch *batch,
 	batch->wr_cnt = 0;
 	batch->need_invalidate_rkey = need_invalidate_rkey;
 	batch->remote_key = remote_key;
+	batch->credit = 0;
 }
 
 static int smbd_send_batch_flush(struct smbdirect_socket *sc,
@@ -1224,7 +1226,7 @@ static int smbd_send_batch_flush(struct smbdirect_socket *sc,
 	int ret = 0;
 
 	if (list_empty(&batch->msg_list))
-		return 0;
+		goto release_credit;
 
 	first = list_first_entry(&batch->msg_list,
 				 struct smbdirect_send_io,
@@ -1266,6 +1268,13 @@ static int smbd_send_batch_flush(struct smbdirect_socket *sc,
 		smbd_free_send_io(last);
 	}
 
+release_credit:
+	if (is_last && !ret && batch->credit) {
+		atomic_add(batch->credit, &sc->send_io.bcredits.count);
+		batch->credit = 0;
+		wake_up(&sc->send_io.bcredits.wait_queue);
+	}
+
 	return ret;
 }
 
@@ -1291,6 +1300,25 @@ static int wait_for_credits(struct smbdirect_socket *sc,
 	} while (true);
 }
 
+static int wait_for_send_bcredit(struct smbdirect_socket *sc,
+				 struct smbdirect_send_batch *batch)
+{
+	int ret;
+
+	if (batch->credit)
+		return 0;
+
+	ret = wait_for_credits(sc,
+			       &sc->send_io.bcredits.wait_queue,
+			       &sc->send_io.bcredits.count,
+			       1);
+	if (ret)
+		return ret;
+
+	batch->credit = 1;
+	return 0;
+}
+
 static int wait_for_send_lcredit(struct smbdirect_socket *sc,
 				 struct smbdirect_send_batch *batch)
 {
@@ -1338,6 +1366,19 @@ static int smbd_post_send_iter(struct smbdirect_socket *sc,
 	struct smbdirect_send_io *request;
 	struct smbdirect_data_transfer *packet;
 	int new_credits = 0;
+	struct smbdirect_send_batch _batch;
+
+	if (!batch) {
+		smbd_send_batch_init(&_batch, false, 0);
+		batch = &_batch;
+	}
+
+	rc = wait_for_send_bcredit(sc, batch);
+	if (rc) {
+		log_outgoing(ERR, "disconnected not sending on wait_bcredit\n");
+		rc = -EAGAIN;
+		goto err_wait_bcredit;
+	}
 
 	rc = wait_for_send_lcredit(sc, batch);
 	if (rc) {
@@ -1432,8 +1473,14 @@ static int smbd_post_send_iter(struct smbdirect_socket *sc,
 		     le32_to_cpu(packet->remaining_data_length));
 
 	rc = smbd_post_send(sc, batch, request);
-	if (!rc)
-		return 0;
+	if (!rc) {
+		if (batch != &_batch)
+			return 0;
+
+		rc = smbd_send_batch_flush(sc, batch, true);
+		if (!rc)
+			return 0;
+	}
 
 err_dma:
 	smbd_free_send_io(request);
@@ -1447,6 +1494,11 @@ static int smbd_post_send_iter(struct smbdirect_socket *sc,
 	wake_up(&sc->send_io.lcredits.wait_queue);
 
 err_wait_lcredit:
+	atomic_add(batch->credit, &sc->send_io.bcredits.count);
+	batch->credit = 0;
+	wake_up(&sc->send_io.bcredits.wait_queue);
+
+err_wait_bcredit:
 	return rc;
 }
 
-- 
2.51.0