[PATCH net v4] rds: ib: Increment i_fastreg_wrs before bailing out

[PATCH net v4] rds: ib: Increment i_fastreg_wrs before bailing out

[Håkon Bugge]

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@vger.kernel.org
Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

---

v3 -> v4:
   * Removed unused "out:" label
   * Added Allison's r-b

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

v1 -> v2: Added Cc: stable@vger.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..bd861191157b5 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
@@ -179,8 +181,10 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
 	 */
 	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

Re: [PATCH net v4] rds: ib: Increment i_fastreg_wrs before bailing out

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 11 Sep 2025 15:33:34 +0200 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net,v4] rds: ib: Increment i_fastreg_wrs before bailing out
    https://git.kernel.org/netdev/net/c/4351ca3fcb3f

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html