[PATCH 6.18 24/49] smb: client: fix last send credit problem causing disconnects

Greg Kroah-Hartman
2026-02-13T13:53:08Z

From: Stefan Metzmacher <metze@samba.org>

commit 93ac432274e1361b4f6cd69e7c5d9b3ac21e13f5 upstream.

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 is a similar logic as we have in the server.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/client/smbdirect.c | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index dbb2d939bc44..20faa6d7f514 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -697,6 +697,15 @@ static void smbd_post_send_credits(struct work_struct *work)

atomic_add(posted, &sc->recv_io.credits.available);

+ /*
+ * If the last send credit is waiting for credits
+ * it can grant we need to wake it up
+ */
+ if (posted &&
+ atomic_read(&sc->send_io.bcredits.count) == 0 &&
+ atomic_read(&sc->send_io.credits.count) == 0)
+ wake_up(&sc->send_io.credits.wait_queue);
+
/* Promptly send an immediate packet as defined in [MS-SMBD] 3.1.1.1 */
if (atomic_read(&sc->recv_io.credits.count) <
sc->recv_io.credits.target - 1) {
@@ -1394,6 +1403,26 @@ static int smbd_post_send_iter(struct smbdirect_socket *sc,
goto err_wait_credit;
}

+ 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);
+ rc = 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)
+ rc = -ENOTCONN;
+ if (rc < 0) {
+ log_outgoing(ERR, "disconnected not sending on last credit\n");
+ rc = -EAGAIN;
+ goto err_wait_credit;
+ }
+
+ new_credits = manage_credits_prior_sending(sc);
+ }
+
request = smbd_alloc_send_io(sc);
if (IS_ERR(request)) {
rc = PTR_ERR(request);
@@ -1448,8 +1477,6 @@ static int smbd_post_send_iter(struct smbdirect_socket *sc,

/* Fill in the packet header */
packet->credits_requested = cpu_to_le16(sp->send_credit_target);
-
- new_credits = manage_credits_prior_sending(sc);
packet->credits_granted = cpu_to_le16(new_credits);

packet->flags = 0;
--
2.53.0