[v1,7/7] sunrpc: Allow keepalive ping on a credit-full transport
diff mbox

Message ID 20170126175628.5794.56813.stgit@manet.1015granger.net
State New
Headers show

Commit Message

Chuck Lever Jan. 26, 2017, 5:56 p.m. UTC
Allow RPC-over-RDMA to send NULL pings even when the transport has
hit its credit limit.

One credit is reserved. It may be used only to send a keepalive
ping.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/linux/sunrpc/sched.h    |    2 ++
 net/sunrpc/xprt.c               |    4 ++++
 net/sunrpc/xprtrdma/transport.c |    4 +++-
 net/sunrpc/xprtrdma/verbs.c     |   13 ++++++++-----
 4 files changed, 17 insertions(+), 6 deletions(-)


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Comments

Anna Schumaker Jan. 30, 2017, 8:29 p.m. UTC | #1
Hi Chuck,

On 01/26/2017 12:56 PM, Chuck Lever wrote:
> Allow RPC-over-RDMA to send NULL pings even when the transport has
> hit its credit limit.
> 
> One credit is reserved. It may be used only to send a keepalive
> ping.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/linux/sunrpc/sched.h    |    2 ++
>  net/sunrpc/xprt.c               |    4 ++++
>  net/sunrpc/xprtrdma/transport.c |    4 +++-
>  net/sunrpc/xprtrdma/verbs.c     |   13 ++++++++-----
>  4 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
> index 7ba040c..a65278e 100644
> --- a/include/linux/sunrpc/sched.h
> +++ b/include/linux/sunrpc/sched.h
> @@ -127,6 +127,7 @@ struct rpc_task_setup {
>  #define RPC_TASK_TIMEOUT	0x1000		/* fail with ETIMEDOUT on timeout */
>  #define RPC_TASK_NOCONNECT	0x2000		/* return ENOTCONN if not connected */
>  #define RPC_TASK_NO_RETRANS_TIMEOUT	0x4000		/* wait forever for a reply */
> +#define RPC_TASK_PRIORITY	0x8000		/* skip congestion control */

This file also defines various RPC_PRIORITY_<whatever> values that get used for the task->tk_priority field.  I wonder if there is a better name for this flag that would help keep people from confusing the two later down the line, but I'm also struggling to come up with anything better.

Thoughts?
Anna

>  
>  #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
>  #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
> @@ -135,6 +136,7 @@ struct rpc_task_setup {
>  #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
>  #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
>  #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
> +#define RPC_HAS_PRIORITY(t)	((t)->tk_flags & RPC_TASK_PRIORITY)
>  
>  #define RPC_TASK_RUNNING	0
>  #define RPC_TASK_QUEUED		1
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index b530a28..e8b7b9f 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -392,6 +392,10 @@ static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *ta
>  {
>  	struct rpc_rqst *req = task->tk_rqstp;
>  
> +	if (RPC_HAS_PRIORITY(task)) {
> +		req->rq_cong = 0;
> +		return 1;
> +	}
>  	if (req->rq_cong)
>  		return 1;
>  	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
> index f97c851..e43cc85 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -538,7 +538,9 @@ static void rpcrdma_keepalive_release(void *calldata)
>  
>  	data = xprt_get(xprt);
>  	null_task = rpc_call_null_helper(task->tk_client, xprt, NULL,
> -					 RPC_TASK_SOFT | RPC_TASK_ASYNC,
> +					 RPC_TASK_SOFT |
> +					 RPC_TASK_ASYNC |
> +					 RPC_TASK_PRIORITY,
>  					 &rpcrdma_keepalive_call_ops, data);
>  	if (!IS_ERR(null_task))
>  		rpc_put_task(null_task);
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 7e14b73..3e218dd 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -136,19 +136,20 @@
>  static void
>  rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
>  {
> -	struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
>  	struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
> +	__be32 *p = rep->rr_rdmabuf->rg_base;
>  	u32 credits;
>  
>  	if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>  		return;
>  
> -	credits = be32_to_cpu(rmsgp->rm_credit);
> +	credits = be32_to_cpup(p + 2);
> +	if (credits > buffer->rb_max_requests)
> +		credits = buffer->rb_max_requests;
> +	/* Reserve one credit for keepalive ping */
> +	credits--;
>  	if (credits == 0)
>  		credits = 1;	/* don't deadlock */
> -	else if (credits > buffer->rb_max_requests)
> -		credits = buffer->rb_max_requests;
> -
>  	atomic_set(&buffer->rb_credits, credits);
>  }
>  
> @@ -914,6 +915,8 @@ struct rpcrdma_rep *
>  	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
>  	int i, rc;
>  
> +	if (r_xprt->rx_data.max_requests < 2)
> +		return -EINVAL;
>  	buf->rb_max_requests = r_xprt->rx_data.max_requests;
>  	buf->rb_bc_srv_max_requests = 0;
>  	atomic_set(&buf->rb_credits, 1);
> 
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Chuck Lever Jan. 30, 2017, 8:32 p.m. UTC | #2
> On Jan 30, 2017, at 3:29 PM, Anna Schumaker <schumaker.anna@gmail.com> wrote:
> 
> Hi Chuck,
> 
> On 01/26/2017 12:56 PM, Chuck Lever wrote:
>> Allow RPC-over-RDMA to send NULL pings even when the transport has
>> hit its credit limit.
>> 
>> One credit is reserved. It may be used only to send a keepalive
>> ping.
>> 
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>> include/linux/sunrpc/sched.h    |    2 ++
>> net/sunrpc/xprt.c               |    4 ++++
>> net/sunrpc/xprtrdma/transport.c |    4 +++-
>> net/sunrpc/xprtrdma/verbs.c     |   13 ++++++++-----
>> 4 files changed, 17 insertions(+), 6 deletions(-)
>> 
>> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
>> index 7ba040c..a65278e 100644
>> --- a/include/linux/sunrpc/sched.h
>> +++ b/include/linux/sunrpc/sched.h
>> @@ -127,6 +127,7 @@ struct rpc_task_setup {
>> #define RPC_TASK_TIMEOUT	0x1000		/* fail with ETIMEDOUT on timeout */
>> #define RPC_TASK_NOCONNECT	0x2000		/* return ENOTCONN if not connected */
>> #define RPC_TASK_NO_RETRANS_TIMEOUT	0x4000		/* wait forever for a reply */
>> +#define RPC_TASK_PRIORITY	0x8000		/* skip congestion control */
> 
> This file also defines various RPC_PRIORITY_<whatever> values that get used for the task->tk_priority field.  I wonder if there is a better name for this flag that would help keep people from confusing the two later down the line, but I'm also struggling to come up with anything better.

PRIORITY was a (lead) trial balloon, and also a sign of weak imagination.

The point of the flag is to bypass congestion control. RPC_TASK_SKIPCONG ?
Meh.


> Thoughts?
> Anna
> 
>> 
>> #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
>> #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
>> @@ -135,6 +136,7 @@ struct rpc_task_setup {
>> #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
>> #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
>> #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
>> +#define RPC_HAS_PRIORITY(t)	((t)->tk_flags & RPC_TASK_PRIORITY)
>> 
>> #define RPC_TASK_RUNNING	0
>> #define RPC_TASK_QUEUED		1
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index b530a28..e8b7b9f 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -392,6 +392,10 @@ static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *ta
>> {
>> 	struct rpc_rqst *req = task->tk_rqstp;
>> 
>> +	if (RPC_HAS_PRIORITY(task)) {
>> +		req->rq_cong = 0;
>> +		return 1;
>> +	}
>> 	if (req->rq_cong)
>> 		return 1;
>> 	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
>> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
>> index f97c851..e43cc85 100644
>> --- a/net/sunrpc/xprtrdma/transport.c
>> +++ b/net/sunrpc/xprtrdma/transport.c
>> @@ -538,7 +538,9 @@ static void rpcrdma_keepalive_release(void *calldata)
>> 
>> 	data = xprt_get(xprt);
>> 	null_task = rpc_call_null_helper(task->tk_client, xprt, NULL,
>> -					 RPC_TASK_SOFT | RPC_TASK_ASYNC,
>> +					 RPC_TASK_SOFT |
>> +					 RPC_TASK_ASYNC |
>> +					 RPC_TASK_PRIORITY,
>> 					 &rpcrdma_keepalive_call_ops, data);
>> 	if (!IS_ERR(null_task))
>> 		rpc_put_task(null_task);
>> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
>> index 7e14b73..3e218dd 100644
>> --- a/net/sunrpc/xprtrdma/verbs.c
>> +++ b/net/sunrpc/xprtrdma/verbs.c
>> @@ -136,19 +136,20 @@
>> static void
>> rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
>> {
>> -	struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
>> 	struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
>> +	__be32 *p = rep->rr_rdmabuf->rg_base;
>> 	u32 credits;
>> 
>> 	if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>> 		return;
>> 
>> -	credits = be32_to_cpu(rmsgp->rm_credit);
>> +	credits = be32_to_cpup(p + 2);
>> +	if (credits > buffer->rb_max_requests)
>> +		credits = buffer->rb_max_requests;
>> +	/* Reserve one credit for keepalive ping */
>> +	credits--;
>> 	if (credits == 0)
>> 		credits = 1;	/* don't deadlock */
>> -	else if (credits > buffer->rb_max_requests)
>> -		credits = buffer->rb_max_requests;
>> -
>> 	atomic_set(&buffer->rb_credits, credits);
>> }
>> 
>> @@ -914,6 +915,8 @@ struct rpcrdma_rep *
>> 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
>> 	int i, rc;
>> 
>> +	if (r_xprt->rx_data.max_requests < 2)
>> +		return -EINVAL;
>> 	buf->rb_max_requests = r_xprt->rx_data.max_requests;
>> 	buf->rb_bc_srv_max_requests = 0;
>> 	atomic_set(&buf->rb_credits, 1);
>> 
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> 
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--
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Anna Schumaker Jan. 30, 2017, 9:36 p.m. UTC | #3
On 01/30/2017 03:32 PM, Chuck Lever wrote:
> 
>> On Jan 30, 2017, at 3:29 PM, Anna Schumaker <schumaker.anna@gmail.com> wrote:
>>
>> Hi Chuck,
>>
>> On 01/26/2017 12:56 PM, Chuck Lever wrote:
>>> Allow RPC-over-RDMA to send NULL pings even when the transport has
>>> hit its credit limit.
>>>
>>> One credit is reserved. It may be used only to send a keepalive
>>> ping.
>>>
>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>> ---
>>> include/linux/sunrpc/sched.h    |    2 ++
>>> net/sunrpc/xprt.c               |    4 ++++
>>> net/sunrpc/xprtrdma/transport.c |    4 +++-
>>> net/sunrpc/xprtrdma/verbs.c     |   13 ++++++++-----
>>> 4 files changed, 17 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
>>> index 7ba040c..a65278e 100644
>>> --- a/include/linux/sunrpc/sched.h
>>> +++ b/include/linux/sunrpc/sched.h
>>> @@ -127,6 +127,7 @@ struct rpc_task_setup {
>>> #define RPC_TASK_TIMEOUT	0x1000		/* fail with ETIMEDOUT on timeout */
>>> #define RPC_TASK_NOCONNECT	0x2000		/* return ENOTCONN if not connected */
>>> #define RPC_TASK_NO_RETRANS_TIMEOUT	0x4000		/* wait forever for a reply */
>>> +#define RPC_TASK_PRIORITY	0x8000		/* skip congestion control */
>>
>> This file also defines various RPC_PRIORITY_<whatever> values that get used for the task->tk_priority field.  I wonder if there is a better name for this flag that would help keep people from confusing the two later down the line, but I'm also struggling to come up with anything better.
> 
> PRIORITY was a (lead) trial balloon, and also a sign of weak imagination.
> 
> The point of the flag is to bypass congestion control. RPC_TASK_SKIPCONG ?

Something like that could work, yeah.

Anna

> Meh.
> 
> 
>> Thoughts?
>> Anna
>>
>>>
>>> #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
>>> #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
>>> @@ -135,6 +136,7 @@ struct rpc_task_setup {
>>> #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
>>> #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
>>> #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
>>> +#define RPC_HAS_PRIORITY(t)	((t)->tk_flags & RPC_TASK_PRIORITY)
>>>
>>> #define RPC_TASK_RUNNING	0
>>> #define RPC_TASK_QUEUED		1
>>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>>> index b530a28..e8b7b9f 100644
>>> --- a/net/sunrpc/xprt.c
>>> +++ b/net/sunrpc/xprt.c
>>> @@ -392,6 +392,10 @@ static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *ta
>>> {
>>> 	struct rpc_rqst *req = task->tk_rqstp;
>>>
>>> +	if (RPC_HAS_PRIORITY(task)) {
>>> +		req->rq_cong = 0;
>>> +		return 1;
>>> +	}
>>> 	if (req->rq_cong)
>>> 		return 1;
>>> 	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
>>> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
>>> index f97c851..e43cc85 100644
>>> --- a/net/sunrpc/xprtrdma/transport.c
>>> +++ b/net/sunrpc/xprtrdma/transport.c
>>> @@ -538,7 +538,9 @@ static void rpcrdma_keepalive_release(void *calldata)
>>>
>>> 	data = xprt_get(xprt);
>>> 	null_task = rpc_call_null_helper(task->tk_client, xprt, NULL,
>>> -					 RPC_TASK_SOFT | RPC_TASK_ASYNC,
>>> +					 RPC_TASK_SOFT |
>>> +					 RPC_TASK_ASYNC |
>>> +					 RPC_TASK_PRIORITY,
>>> 					 &rpcrdma_keepalive_call_ops, data);
>>> 	if (!IS_ERR(null_task))
>>> 		rpc_put_task(null_task);
>>> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
>>> index 7e14b73..3e218dd 100644
>>> --- a/net/sunrpc/xprtrdma/verbs.c
>>> +++ b/net/sunrpc/xprtrdma/verbs.c
>>> @@ -136,19 +136,20 @@
>>> static void
>>> rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
>>> {
>>> -	struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
>>> 	struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
>>> +	__be32 *p = rep->rr_rdmabuf->rg_base;
>>> 	u32 credits;
>>>
>>> 	if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>>> 		return;
>>>
>>> -	credits = be32_to_cpu(rmsgp->rm_credit);
>>> +	credits = be32_to_cpup(p + 2);
>>> +	if (credits > buffer->rb_max_requests)
>>> +		credits = buffer->rb_max_requests;
>>> +	/* Reserve one credit for keepalive ping */
>>> +	credits--;
>>> 	if (credits == 0)
>>> 		credits = 1;	/* don't deadlock */
>>> -	else if (credits > buffer->rb_max_requests)
>>> -		credits = buffer->rb_max_requests;
>>> -
>>> 	atomic_set(&buffer->rb_credits, credits);
>>> }
>>>
>>> @@ -914,6 +915,8 @@ struct rpcrdma_rep *
>>> 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
>>> 	int i, rc;
>>>
>>> +	if (r_xprt->rx_data.max_requests < 2)
>>> +		return -EINVAL;
>>> 	buf->rb_max_requests = r_xprt->rx_data.max_requests;
>>> 	buf->rb_bc_srv_max_requests = 0;
>>> 	atomic_set(&buf->rb_credits, 1);
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>> --
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>> the body of a message to majordomo@vger.kernel.org
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> 
> --
> Chuck Lever
> 
> 
> 
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Patch
diff mbox

diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
index 7ba040c..a65278e 100644
--- a/include/linux/sunrpc/sched.h
+++ b/include/linux/sunrpc/sched.h
@@ -127,6 +127,7 @@  struct rpc_task_setup {
 #define RPC_TASK_TIMEOUT	0x1000		/* fail with ETIMEDOUT on timeout */
 #define RPC_TASK_NOCONNECT	0x2000		/* return ENOTCONN if not connected */
 #define RPC_TASK_NO_RETRANS_TIMEOUT	0x4000		/* wait forever for a reply */
+#define RPC_TASK_PRIORITY	0x8000		/* skip congestion control */
 
 #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
 #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
@@ -135,6 +136,7 @@  struct rpc_task_setup {
 #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
 #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
 #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
+#define RPC_HAS_PRIORITY(t)	((t)->tk_flags & RPC_TASK_PRIORITY)
 
 #define RPC_TASK_RUNNING	0
 #define RPC_TASK_QUEUED		1
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index b530a28..e8b7b9f 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -392,6 +392,10 @@  static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *ta
 {
 	struct rpc_rqst *req = task->tk_rqstp;
 
+	if (RPC_HAS_PRIORITY(task)) {
+		req->rq_cong = 0;
+		return 1;
+	}
 	if (req->rq_cong)
 		return 1;
 	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index f97c851..e43cc85 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -538,7 +538,9 @@  static void rpcrdma_keepalive_release(void *calldata)
 
 	data = xprt_get(xprt);
 	null_task = rpc_call_null_helper(task->tk_client, xprt, NULL,
-					 RPC_TASK_SOFT | RPC_TASK_ASYNC,
+					 RPC_TASK_SOFT |
+					 RPC_TASK_ASYNC |
+					 RPC_TASK_PRIORITY,
 					 &rpcrdma_keepalive_call_ops, data);
 	if (!IS_ERR(null_task))
 		rpc_put_task(null_task);
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 7e14b73..3e218dd 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -136,19 +136,20 @@ 
 static void
 rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
 {
-	struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
 	struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
+	__be32 *p = rep->rr_rdmabuf->rg_base;
 	u32 credits;
 
 	if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
 		return;
 
-	credits = be32_to_cpu(rmsgp->rm_credit);
+	credits = be32_to_cpup(p + 2);
+	if (credits > buffer->rb_max_requests)
+		credits = buffer->rb_max_requests;
+	/* Reserve one credit for keepalive ping */
+	credits--;
 	if (credits == 0)
 		credits = 1;	/* don't deadlock */
-	else if (credits > buffer->rb_max_requests)
-		credits = buffer->rb_max_requests;
-
 	atomic_set(&buffer->rb_credits, credits);
 }
 
@@ -914,6 +915,8 @@  struct rpcrdma_rep *
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
 	int i, rc;
 
+	if (r_xprt->rx_data.max_requests < 2)
+		return -EINVAL;
 	buf->rb_max_requests = r_xprt->rx_data.max_requests;
 	buf->rb_bc_srv_max_requests = 0;
 	atomic_set(&buf->rb_credits, 1);