Re: [PATCH net v3] rds: ib: Increment i_fastreg_wrs before bailing out

Haakon Bugge
2025-09-11T13:26:16Z

Hi Allison,

> On 10 Sep 2025, at 20:47, Allison Henderson <allison.henderson@oracle.com> wrote:
>
> On Wed, 2025-09-10 at 13:04 +0200, Håkon Bugge 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.
> Hi Håkon,
>
> This sounds much clearer, thank you!
>
>>
>> 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>
>>
>> ---
>>
>> 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..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;
> Just one nit: This was the only place the out label was used isnt it? If so, lets go ahead and clear it out.

That is indeed true!

>
>> + 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:
> With that fixed, you can go ahead and add my rvb:
> Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

Will do, thanks for the r-b!

Håkon

>
> Thank you!
>
>> + return ret;
>>
>> +out_inc:
>> + atomic_inc(&ibmr->ic->i_fastreg_wrs);
>> return ret;
>> }