Messages in this thread |  | | | Date | Mon, 29 Jun 2009 12:53:48 +0300 | | From | Avi Kivity <> | | Subject | Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus |
On 06/29/2009 12:41 PM, Michael S. Tsirkin wrote: > On Mon, Jun 29, 2009 at 11:37:00AM +0300, Avi Kivity wrote: > >> On 06/28/2009 10:34 PM, Michael S. Tsirkin wrote: >> >>> This changes bus accesses to use high-level kvm_io_bus_read/kvm_io_bus_write >>> functions, which utilize read/write semaphore intead of mutex. in_range now >>> becomes unused so it is removed from device ops in favor of read/write >>> callbacks performing range checks internally. >>> >>> This allows aliasing (mostly for in-kernel virtio), as well as better error >>> handling by making it possible to pass errors up to userspace. And it's enough >>> to look at the diffstat to see that it's a better API anyway. >>> >>> While we are at it, document locking rules for kvm_io_device_ops. >>> >>> Note: since the use of the new bus_lock is localized to a small number of >>> places, it will be easy to switch to srcu in the future if we so desire. >>> >>> >> Looks good. But please split into a locking change patch and an API >> change patch (in whatever order makes more sense). >> > > This is harder than it seems. Is this really important? > > The locking change itself is about 6 lines, but > 1. if I do it after in_range removal I get deadlocks > as after marcelo's change kvm->lock is taken internally by writers. >
slots_lock is an outer lock to kvm->lock.
> 2. if I do it before in_range removal it's a lot of churn: > one of the reasons for code reorg is so that there are less > places to change locking. > > >
I don't think you really need to change anything. slots_lock is already taken (except where you modify the list).
How about this:
1. add slots_lock for write when modifying the list 2. change the api 3. drop kvm->lock
?
-- error compiling committee.c: too many arguments to function
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