Re: BUG at net/sunrpc/svc_xprt.c:921

[Stanislav Kinsbursky]

18.01.2013 03:41, Mark Lord ÐÐÑÐÑ:
> On 13-01-17 08:24 AM, Stanislav Kinsbursky wrote:
> ..
> > This looks like the old issue I was trying to fix with "SUNRPC: protect service sockets lists during
> > per-net shutdown".
> > So, here is the problem as I see it: there is a transport, which is processed by service thread and
> > it's processing is racing with per-net service shutdown:
> >
> > CPU#0:                            CPU#1:
> >
> > svc_recv                        svc_close_net
> > svc_get_next_xprt (list_del_init(xpt_ready))
> >                              svc_close_list (set XPT_BUSY and XPT_CLOSE)
> >                              svc_clear_pools(xprt was gained on CPU#0 already)
> >                              svc_delete_xprt (set XPT_DEAD)
> > svc_handle_xprt (is XPT_CLOSE => svc_delete_xprt()
> > BUG()
> >
> > So, from my POW, we need some way to:
> > 1) Skip such in-progress transports on svc_close_net() call (there is not way to detect them, or at
> > least I don't see one)
> > 2) Delete the transport after somewhere after svc_xprt_received()
> >
> > But there is a problem with svc_xprt_received(): there is a call for svc_xprt_put() in it
> > (svc_recv->svc_handle_xprt->svc_xprt_received->svc_xprt_put) . And if we are the only user - then
> > the transport will be destroyed. But transport is dereferenced later in svc_recv() after the
> > svc_handle_xprt call.
>
> Sounds like a reference count type of problem/solution (kref) (?)

No, it would be very simple.
Unluckily, the problem is more complex. In few words, the problem is in dynamic resources (transports) creation/attaching
and destruction/detaching for running (!) SUNRPC service.
You have more than one NFS mount in different network namespaces, haven't you?

--
Best regards,
Stanislav Kinsbursky
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