Re: [Xen-devel] [PATCH] gntdev: switch back to rwlocks

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 09.07.10 at 16:32, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> 
>>> wrote:
> Hi Jeremy,
> this patch switches back from spinlocks to rwlocks in gntdev, solving
> the locking issue that was preventing stubdoms from working.
> In particular the problem is that gntdev_mmap calls apply_to_page_range
> after acquiring the spinlock. apply_to_page_range causes the mmu
> notifiers to be called, so mn_invl_range_start will be called that will
> try to acquire again the same spinlock.

Shouldn't this be solved in a way not depending on an implementation
detail (rw-locks being unfair in that readers can lock out writers
indefinitely)? Is it even certain that all arch-es implement rw-locks
in a manner compatible with this?

Jan


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