Re: [Xen-devel][Pv-ops][PATCH] Netback multiple tasklet support

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2010-01-13 at 10:17 +0000, Jan Beulich wrote:
> >>> Ian Campbell <Ian.Campbell@xxxxxxxxxx> 10.12.09 10:07 >>>
> >Subject: xen: ensure locking gnttab_copy_grant_page is safe against 
> >interrupts.
> >
> >Now that netback processing occurs in a thread instead of a tasklet
> >gnttab_copy_grant_page needs to be safe against interrupts.
> >
> >The code is currently commented out in this tree but on 2.6.18 we observed a
> >deadlock where the netback thread called gnttab_copy_grant_page, locked
> >gnttab_dma_lock for writing, was interrupted and on return from interrupt the
> >network stack's TX tasklet ended up calling __gnttab_dma_map_page via the
> >hardware driver->swiotlb and tries to take gnttab_dma_lock for reading.
> >
> >Correct the commented code so we don't get bitten if/when it is re-enabled.
> 
> Wouldn't safe-against-softirq be sufficient then?

Yes, I guess so.

> Or if not (i.e. if meant to be generic), wouldn't the irq-safe variant need 
> to be used
> independent of the new feature (and then also in the 2.6.18 tree)?

Ian.


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