From 66c082e3d4651e8629a393a9e182b01eb50fb0a3 Mon Sep 17 00:00:00 2001 From: Stefan Metzmacher Date: Thu, 22 Jan 2026 18:16:43 +0100 Subject: [PATCH] smb: server: make use of smbdirect_socket.recv_io.credits.available commit 26ad87a2cfb8c1384620d1693a166ed87303046e upstream. The logic off managing recv credits by counting posted recv_io and granted credits is racy. That's because the peer might already consumed a credit, but between receiving the incoming recv at the hardware and processing the completion in the 'recv_done' functions we likely have a window where we grant credits, which don't really exist. So we better have a decicated counter for the available credits, which will be incremented when we posted new recv buffers and drained when we grant the credits to the peer. This fixes regression Namjae reported with the 6.18 release. Fixes: 89b021a72663 ("smb: server: manage recv credits by counting posted recv_io and granted credits") Cc: # 6.18.x Cc: Namjae Jeon Cc: Steve French Cc: Tom Talpey Cc: linux-cifs@vger.kernel.org Cc: samba-technical@lists.samba.org Signed-off-by: Stefan Metzmacher Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman --- fs/smb/server/transport_rdma.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/fs/smb/server/transport_rdma.c b/fs/smb/server/transport_rdma.c index 7d2ad73839e8..de959ca91f3e 100644 --- a/fs/smb/server/transport_rdma.c +++ b/fs/smb/server/transport_rdma.c @@ -926,6 +926,8 @@ static void smb_direct_post_recv_credits(struct work_struct *work) } } + atomic_add(credits, &sc->recv_io.credits.available); + if (credits) queue_work(sc->workqueue, &sc->idle.immediate_work); } @@ -972,19 +974,37 @@ static void send_done(struct ib_cq *cq, struct ib_wc *wc) static int manage_credits_prior_sending(struct smbdirect_socket *sc) { + int missing; + int available; int new_credits; if (atomic_read(&sc->recv_io.credits.count) >= sc->recv_io.credits.target) return 0; - new_credits = atomic_read(&sc->recv_io.posted.count); - if (new_credits == 0) + missing = (int)sc->recv_io.credits.target - atomic_read(&sc->recv_io.credits.count); + available = atomic_xchg(&sc->recv_io.credits.available, 0); + new_credits = (u16)min3(U16_MAX, missing, available); + if (new_credits <= 0) { + /* + * If credits are available, but not granted + * we need to re-add them again. + */ + if (available) + atomic_add(available, &sc->recv_io.credits.available); return 0; + } - new_credits -= atomic_read(&sc->recv_io.credits.count); - if (new_credits <= 0) - return 0; + if (new_credits < available) { + /* + * Readd the remaining available again. + */ + available -= new_credits; + atomic_add(available, &sc->recv_io.credits.available); + } + /* + * Remember we granted the credits + */ atomic_add(new_credits, &sc->recv_io.credits.count); return new_credits; }