On Nov 18, 2014, at 3:10 PM, Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Wed, Nov 12, 2014 at 09:41:28PM -0500, Jeff Layton wrote:
>> On Wed, 12 Nov 2014 18:04:04 -0500
>> Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>>
>>> Both xprt_lookup_rqst() and xprt_complete_rqst() require that you
>>> take the transport lock in order to avoid races with xprt_transmit().
>
> Thanks, looks right.
>
> Have you seen this in practice? (I'm just wondering whether it's worth
> a stable cc:.)
Since the backchannel has a single slot, I wonder if it
would be possible to race here.
> --b.
>
>>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>>> Cc: Bruce Fields <bfields@xxxxxxxxxxxx>
>>> ---
>>> net/sunrpc/svcsock.c | 27 ++++++++++++++++-----------
>>> 1 file changed, 16 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>>> index 3f959c681885..f9c052d508f0 100644
>>> --- a/net/sunrpc/svcsock.c
>>> +++ b/net/sunrpc/svcsock.c
>>> @@ -1019,17 +1019,12 @@ static int receive_cb_reply(struct svc_sock *svsk, struct svc_rqst *rqstp)
>>> xid = *p++;
>>> calldir = *p;
>>>
>>> - if (bc_xprt)
>>> - req = xprt_lookup_rqst(bc_xprt, xid);
>>> -
>>> - if (!req) {
>>> - printk(KERN_NOTICE
>>> - "%s: Got unrecognized reply: "
>>> - "calldir 0x%x xpt_bc_xprt %p xid %08x\n",
>>> - __func__, ntohl(calldir),
>>> - bc_xprt, ntohl(xid));
>>> + if (!bc_xprt)
>>> return -EAGAIN;
>>> - }
>>> + spin_lock_bh(&bc_xprt->transport_lock);
>>> + req = xprt_lookup_rqst(bc_xprt, xid);
>>> + if (!req)
>>> + goto unlock_notfound;
>>>
>>> memcpy(&req->rq_private_buf, &req->rq_rcv_buf, sizeof(struct xdr_buf));
>>> /*
>>> @@ -1040,11 +1035,21 @@ static int receive_cb_reply(struct svc_sock *svsk, struct svc_rqst *rqstp)
>>> dst = &req->rq_private_buf.head[0];
>>> src = &rqstp->rq_arg.head[0];
>>> if (dst->iov_len < src->iov_len)
>>> - return -EAGAIN; /* whatever; just giving up. */
>>> + goto unlock_eagain; /* whatever; just giving up. */
>>> memcpy(dst->iov_base, src->iov_base, src->iov_len);
>>> xprt_complete_rqst(req->rq_task, rqstp->rq_arg.len);
>>> rqstp->rq_arg.len = 0;
>>> + spin_unlock_bh(&bc_xprt->transport_lock);
>>> return 0;
>>> +unlock_notfound:
>>> + printk(KERN_NOTICE
>>> + "%s: Got unrecognized reply: "
>>> + "calldir 0x%x xpt_bc_xprt %p xid %08x\n",
>>> + __func__, ntohl(calldir),
>>> + bc_xprt, ntohl(xid));
>>> +unlock_eagain:
>>> + spin_unlock_bh(&bc_xprt->transport_lock);
>>> + return -EAGAIN;
>>> }
>>>
>>> static int copy_pages_to_kvecs(struct kvec *vec, struct page **pages, int len)
>>
>> Nice catch. It would also be good to pair this with a
>> lockdep_assert_held() call in xprt_lookup_rqst, but that could be added
>> in a separate patch.
>>
>> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> --
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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