Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

[Tom Tucker <tom@opengridcomputing.com>]

Please disregard this mail! I fixed a relayhost parameter in a lab 
machine and this queued mail was sent. My apologies.

Tom

J. Bruce Fields wrote:
> On Mon, Jul 27, 2009 at 05:33:55PM -0400, bfields wrote:
>   
>> On Tue, Aug 12, 2008 at 05:13:04PM -0500, Tom Tucker wrote:
>>     
>>> RDMA_READ completions are kept on a separate queue from the general
>>> I/O request queue. Since a separate lock is used to protect the RDMA_READ
>>> completion queue, a race exists between the dto_tasklet and the
>>> svc_rdma_recvfrom thread where the dto_tasklet sets the XPT_DATA
>>> bit and adds I/O to the read-completion queue. Concurrently, the
>>> recvfrom thread checks the generic queue, finds it empty and resets
>>> the XPT_DATA bit. A subsequent svc_xprt_enqueue will fail to enqueue
>>> the transport for I/O and cause the transport to "stall".
>>>
>>> The fix is to protect both lists with the same lock and set the XPT_DATA
>>> bit with this lock held.
>>>       
>> Thanks.  Assuming this race has existed from the start (so it's not a
>> recent regression), and the consequences are no worse than a stall, I'm
>> inclined to queue this up for 2.6.32--but if I'm wrong about either of
>> those, we could try for 2.6.31 and/or stable.
>>     
>
> Erp, cripes, sorry--only just noticed all this mail seems to have been
> delayed a year!  OK....--b.
>
>   
>> --b.
>>
>>     
>>> Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
>>>
>>> ---
>>>  include/linux/sunrpc/svc_rdma.h          |    1 -
>>>  net/sunrpc/xprtrdma/svc_rdma_recvfrom.c  |    8 ++++----
>>>  net/sunrpc/xprtrdma/svc_rdma_transport.c |    5 ++---
>>>  3 files changed, 6 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>>> index ef2e3a2..dc05b54 100644
>>> --- a/include/linux/sunrpc/svc_rdma.h
>>> +++ b/include/linux/sunrpc/svc_rdma.h
>>> @@ -143,7 +143,6 @@ struct svcxprt_rdma {
>>>  	unsigned long	     sc_flags;
>>>  	struct list_head     sc_dto_q;		/* DTO tasklet I/O pending Q */
>>>  	struct list_head     sc_read_complete_q;
>>> -	spinlock_t           sc_read_complete_lock;
>>>  	struct work_struct   sc_work;
>>>  };
>>>  /* sc_flags */
>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> index b4b17f4..74de31a 100644
>>> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> @@ -443,18 +443,18 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
>>>  
>>>  	dprintk("svcrdma: rqstp=%p\n", rqstp);
>>>  
>>> -	spin_lock_bh(&rdma_xprt->sc_read_complete_lock);
>>> +	spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
>>>  	if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
>>>  		ctxt = list_entry(rdma_xprt->sc_read_complete_q.next,
>>>  				  struct svc_rdma_op_ctxt,
>>>  				  dto_q);
>>>  		list_del_init(&ctxt->dto_q);
>>>  	}
>>> -	spin_unlock_bh(&rdma_xprt->sc_read_complete_lock);
>>> -	if (ctxt)
>>> +	if (ctxt) {
>>> +		spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
>>>  		return rdma_read_complete(rqstp, ctxt);
>>> +	}
>>>  
>>> -	spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
>>>  	if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
>>>  		ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
>>>  				  struct svc_rdma_op_ctxt,
>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> index 19ddc38..900cb69 100644
>>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> @@ -359,11 +359,11 @@ static void sq_cq_reap(struct svcxprt_rdma *xprt)
>>>  			if (test_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags)) {
>>>  				struct svc_rdma_op_ctxt *read_hdr = ctxt->read_hdr;
>>>  				BUG_ON(!read_hdr);
>>> +				spin_lock_bh(&xprt->sc_rq_dto_lock);
>>>  				set_bit(XPT_DATA, &xprt->sc_xprt.xpt_flags);
>>> -				spin_lock_bh(&xprt->sc_read_complete_lock);
>>>  				list_add_tail(&read_hdr->dto_q,
>>>  					      &xprt->sc_read_complete_q);
>>> -				spin_unlock_bh(&xprt->sc_read_complete_lock);
>>> +				spin_unlock_bh(&xprt->sc_rq_dto_lock);
>>>  				svc_xprt_enqueue(&xprt->sc_xprt);
>>>  			}
>>>  			svc_rdma_put_context(ctxt, 0);
>>> @@ -428,7 +428,6 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
>>>  	init_waitqueue_head(&cma_xprt->sc_send_wait);
>>>  
>>>  	spin_lock_init(&cma_xprt->sc_lock);
>>> -	spin_lock_init(&cma_xprt->sc_read_complete_lock);
>>>  	spin_lock_init(&cma_xprt->sc_rq_dto_lock);
>>>  
>>>  	cma_xprt->sc_ord = svcrdma_ord;
>>>       
> --
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