linux-kernel - [PATCH net v3] rds: ib: Increment i_fastreg

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Message-ID: <20250910110501.350238-1-haakon.bugge@oracle.com>
Date: Wed, 10 Sep 2025 13:04:59 +0200
From: Håkon Bugge <haakon.bugge@...cle.com>
To: Allison Henderson <allison.henderson@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: stable@...r.kernel.org,
        Håkon Bugge <haakon.bugge@...cle.com>,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: [PATCH net v3] rds: ib: Increment i_fastreg_wrs before bailing out

We need to increment i_fastreg_wrs before we bail out from
rds_ib_post_reg_frmr().

We have a fixed budget of how many FRWR operations that can be
outstanding using the dedicated QP used for memory registrations and
de-registrations. This budget is enforced by the atomic_t
i_fastreg_wrs. If we bail out early in rds_ib_post_reg_frmr(), we will
"leak" the possibility of posting an FRWR operation, and if that
accumulates, no FRWR operation can be carried out.

Fixes: 1659185fb4d0 ("RDS: IB: Support Fastreg MR (FRMR) memory registration mode")
Fixes: 3a2886cca703 ("net/rds: Keep track of and wait for FRWR segments in use upon shutdown")
Cc: stable@...r.kernel.org
Signed-off-by: Håkon Bugge <haakon.bugge@...cle.com>

---

v2 -> v3:
   * Amended commit message
   * Removed indentation of this section
   * Fixing error path from ib_post_send()

v1 -> v2: Added Cc: stable@...r.kernel.org
---
 net/rds/ib_frmr.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/net/rds/ib_frmr.c b/net/rds/ib_frmr.c
index 28c1b00221780..395a99b5a65ca 100644
--- a/net/rds/ib_frmr.c
+++ b/net/rds/ib_frmr.c
@@ -133,12 +133,15 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
 
 	ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_dma_len,
 				&off, PAGE_SIZE);
-	if (unlikely(ret != ibmr->sg_dma_len))
-		return ret < 0 ? ret : -EINVAL;
+	if (unlikely(ret != ibmr->sg_dma_len)) {
+		ret = ret < 0 ? ret : -EINVAL;
+		goto out_inc;
+	}
 
-	if (cmpxchg(&frmr->fr_state,
-		    FRMR_IS_FREE, FRMR_IS_INUSE) != FRMR_IS_FREE)
-		return -EBUSY;
+	if (cmpxchg(&frmr->fr_state, FRMR_IS_FREE, FRMR_IS_INUSE) != FRMR_IS_FREE) {
+		ret = -EBUSY;
+		goto out_inc;
+	}
 
 	atomic_inc(&ibmr->ic->i_fastreg_inuse_count);
 
@@ -166,11 +169,10 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
 		/* Failure here can be because of -ENOMEM as well */
 		rds_transition_frwr_state(ibmr, FRMR_IS_INUSE, FRMR_IS_STALE);
 
-		atomic_inc(&ibmr->ic->i_fastreg_wrs);
 		if (printk_ratelimit())
 			pr_warn("RDS/IB: %s returned error(%d)\n",
 				__func__, ret);
-		goto out;
+		goto out_inc;
 	}
 
 	/* Wait for the registration to complete in order to prevent an invalid
@@ -178,9 +180,11 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
 	 * being accessed while registration is still pending.
 	 */
 	wait_event(frmr->fr_reg_done, !frmr->fr_reg);
-
 out:
+	return ret;
 
+out_inc:
+	atomic_inc(&ibmr->ic->i_fastreg_wrs);
 	return ret;
 }
 
-- 
2.43.5