Re: [Xen-devel] netfront leaking two pages on unload?

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 18/1/08 20:35, "Andy Grover" <andy.grover@xxxxxxxxxx> wrote:

> Thanks for taking a look.
> 
> I was going to put together a patch to properly free the 2 pages in
> netfront, but it looks like this is already handled inside
> gnttab_end_foreign_access().
> 
> It seems a little non-intuitive that gnttab_end_foreign_access doesn't
> just end foreign access, it frees the page too. This leads to what
> confused me -- a driver allocating a page but (seemingly) never freeing
> it.
> 
> I think it might be clearer to make callers explicitly free the page
> after checking gnttab_end_foreign_access's return val for success. Would
> you accept a patch doing this, or are there other reasons for the
> current code?

If the grant is not yet unmapped by the backend then the gnttab subsystem in
the frontend OS should take responsibility for freeing the page at the
appropriate time in the future (i.e., when the grant does become unmapped).
We don't want to leave that to the frontend driver itself because it would
result in code duplication in every driver, and also the driver may be
unloaded before the page can be freed.

 -- Keir



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