Re: [Xen-devel] [PATCH 4/4] [Net] Support accelerated network plugin modules

["Zhu Han" <schumi.han@xxxxxxxxx>]

On 6/15/07, Kieran Mansley <kmansley@xxxxxxxxxxxxxx> wrote:
> The lock protects the use_count variable.  The use_count variable
> prevents the plugin module unloading while it is being used.  I couldn't
> just use the lock to prevent the module unloading as the hook function
> (i) might block (and holding a spin_lock would be rather antisocial)
> (ii) might call back into netfront and try to take the lock again, which
> would deadlock.
If the hook routine blocks on the other code path instead of tx/rx
path,  why not use a simple atomic reference count. When the reference
count reachs zero, free it. Considering you can synchronzie on tx/rx
path, the free will not happen under the critical code path. So the
uninitialize work could be done inside the free routine even if it
blocks.

> I think that RCU would only work in this situation if the hook functions
> didn't block,.
I agree.

> Kieran

--
best regards,
hanzhu

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