On Mon, Jul 27, 2009 at 04:43:21PM -0500, Tom Tucker wrote:
> Please disregard this mail! I fixed a relayhost parameter in a lab
> machine and this queued mail was sent. My apologies.
No problem! I didn't recognize that first patch, but then got to the
following series and said hey, wait a minute, we already did this....
--b.
>
> 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@xxxxxxxxxxxxxxxxxxxxx>
>>>>
>>>> ---
>>>> 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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