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