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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> 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? 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)?

Jan


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