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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 12/10/09 01:07, Ian Campbell wrote:
> 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.
>    
What's the issue here?  I'm inclined to just remove the commented-out 
code if it isn't being used, and re-evaluate the locking if/when it 
becomes necessary.
    J

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