Re: [PATCH] xprtrdma: take vendor driver refcount at client

[Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On 7/28/2015 2:01 AM, Devesh Sharma wrote:
> Thanks Chuck Lever for the valuable feedback and suggestions.
>
> This is a rework of the following patch sent almost a year back:
> http://www.mail-archive.com/linux-rdma%40vger.kernel.org/msg20730.html
>
> In presence of active mount if someone tries to rmmod vendor-driver, the
> command remains stuck forever waiting for destruction of all rdma-cm-id.
> in worst case client can crash during shutdown with active mounts.

Ouch, taking a reference on the module preventing it from unloading is
not very well behaved (putting it nicely). That's also breaking the
layering of ULPs <-> core <-> provider scheme.

Why not just cleanup everything upon DEVICE_REMOVAL?

>
> The existing code assumes that ia->ri_id->device cannot change during
> the lifetime of a transport. Lifting that assumption is a long chain
> of work, and is in plan.
>
> The community decided that preventing the hang right now is more
> important than waiting for architectural changes.

Well, if you are putting a bandage here - the code should be documented
with a proper FIXME.
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