Thanks Dan and Bill for the quick response. As Dan suggested, is moving
svc_rqst_xprt_register() to the end
of svc_vc_rendezvous()
the
right
fix?
On Thu, Aug 31, 2017 at 8:30 AM, William Allen Simpson <
william.allen.simp...@gmail.com> wrote:
> On 8/31/17 9:14 AM, Daniel Gryniewicz wrote:
>
>> On 08/30/2017 10:06 PM, Pradeep wrote:
>>
>>> Hi all,
>>>
>>> I'm hitting a crash in TIRPC with Ganesha 2.6-dev.5. It appears to me
>>> that there is a race between a incoming RPC message on a new xprt (for
>>> which accept() was done on the FD) and TIRPC setting the process_cb on the
>>> new xprt.
>>>
>>> We set the xprt->xp_dispatch.process_cb() from the rendezvous function
>>> (nfs_rpc_dispatch_tcp_NFS in case of NFS/TCP). This is called at the end of
>>> svc_vc_rendezvous(). But before this happens an RPC request could be
>>> invoking svc_vc_recv() because we have already called accept(). Shouldn't
>>> we setup xprt before accept()?
>>>
>>
>> Not the accept itself, but adding the accepted fd to epoll, which is also
>> happening before the rendezvous. I think the call to
>> svc_rqst_xprt_register() needs to be last, or a lock needs to be taken.
>>
>> Bill?
>>
>> Yes, that's a problem. I checked v2.5 (ntirpc 1.5) and that has the
> same issue. It's registering the epoll before doing other essential
> things, like setting up the recvsize and sendsize, and calling (old)
> xp_recv_user_data (now named nfs_rpc_dispatch_tcp_NFS).
>
> My guess is you're seeing it because the 2.6 epoll loop is much faster.
> We're expecting to find more of these timing and code ordering errors.
>
> But it looks like a relatively easy fix.
>
> Thanks for the excellent detailed report. So helpful!
>
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