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xen-devel
Re: [Xen-devel][Pv-ops][PATCH] Netback multiple tasklet support
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To: |
Jan Beulich <JBeulich@xxxxxxxxxx> |
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Subject: |
Re: [Xen-devel][Pv-ops][PATCH] Netback multiple tasklet support |
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From: |
Ian Campbell <Ian.Campbell@xxxxxxxxxx> |
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Date: |
Thu, 14 Jan 2010 16:55:37 +0000 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Xu <dongxiao.xu@xxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Steven Smith <Steven.Smith@xxxxxxxxxxxxx>, Dongxiao |
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Thu, 14 Jan 2010 08:57:15 -0800 |
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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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