Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux