On 1/14/20 4:45 AM, Jason Gunthorpe wrote:
On Mon, Jan 13, 2020 at 02:44:52PM -0800, Ralph Campbell wrote:
I'm using the device driver lock to serialize find/insert/update/remove changes to the interval tree.
The device driver lock can't really fully serialize this as it doesn't effect how the intersection lookup runs.
Jason
Single updates to the interval notifier are atomic due to the struct mmu_notifier_mm spinlock so the issue is with "punching a hole" in the interval. In that case, the existing interval is updated to cover one side of the hole and a new interval is inserted for the other side while holding the driver lock.
Since this sequence is done from the invalidate() callback, those two operations will be deferred until the callback returns and any other parallel invalidates complete (which would be serialized on the driver lock). So none of these changes will be visible to the interval tree walks until the last invalidate task calls mn_itree_inv_end() and all the deferred changes are applied atomically while holding the spinlock. I'll make sure to add comments explaining this.
But I see your point if this sequence is done outside of the invalidate callback. In that case, if the driver shrank the interval, an invalidate callback for the right hand side could be missed before the insertion of the new interval for the right hand side. I'll explain this in the comments for nouveau_svmm_do_unmap() and dmirror_do_unmap().