On Thu, 03 Oct 2019, Jason Gunthorpe wrote:
On Thu, Oct 03, 2019 at 01:18:47PM -0700, Davidlohr Bueso wrote:Hi, It has been discussed[1,2] that almost all users of interval trees would better be served if the intervals were actually not [a,b], but instead [a, b). This series attempts to convert all callers by way of transitioning from using "interval_tree_generic.h" to "interval_tree_gen.h". Once all users are converted, we remove the former. Patch 1: adds a call that will make patch 8 easier to review by introducing stab queries for the vma interval tree. Patch 2: adds the new interval_tree_gen.h which is the same as the old one but uses [a,b) intervals. Patch 3-9: converts, in baby steps (as much as possible), each interval tree to the new [a,b) one. It is done this way also to maintain bisectability. Most conversions are pretty straightforward, however, there are some creative ways in which some callers use the interval 'end' when going through intersecting ranges within a tree. Ie: patch 3, 6 and 9. Patch 10: deletes the interval_tree_generic.h header; there are no longer any users. Patch 11: finally simplifies x86 pat tree to use the new interval tree machinery. This has been lightly tested, and certainly not on driver paths that do non trivial conversions. Also needs more eyeballs as conversions can be easily missed (even when I've tried mitigating this by renaming the endpoint from 'last' to 'end' in each corresponding structure). Because this touches a lot of drivers, I'm Cc'ing the whole thing to a couple of relevant lists (mm, dri, rdma); sorry if you consider this spam. Applies on top of today's linux-next tree. Please consider for v5.5. Thanks! [1] https://lore.kernel.org/lkml/CANN689HVDJXKEwB80yPAVwvRwnV4HfiucQVAho=dupKM_iKozw@xxxxxxxxxxxxxx/Hurm, this is not entirely accurate. Most users do actually want overlapping and multiple ranges. I just studied this extensively: radeon_mn actually wants overlapping but seems to mis-understand the interval_tree API and actively tries hard to prevent overlapping at great cost and complexity. I have a patch to delete all of this and just be overlapping. amdgpu_mn copied the wrongness from radeon_mn All the DRM drivers are basically the same here, tracking userspace controlled VAs, so overlapping is essential hfi1/mmu_rb definitely needs overlapping as it is dealing with userspace VA ranges under control of userspace. As do the other infiniband users. vhost probably doesn't overlap in the normal case, but again userspace could trigger overlap in some pathalogical case. The [start,last] allows the interval to cover up to ULONG_MAX. I don't know if this is needed however. Many users are using userspace VAs here. Is there any kernel configuration where ULONG_MAX is a valid userspace pointer? Ie 32 bit 4G userspace? I don't know. Many users seemed to have bugs where they were taking a userspace controlled start + length and converting them into a start/end for interval tree without overflow protection (woops) Also I have a series already cooking to delete several of these interval tree users, which will terribly conflict with this :\
I have no problem redoing after your changes; if it's worth it at all.
Is it really necessary to make such churn for such a tiny API change?
I agree, and was kind of expecting this. In general the diffstat ended up being larger than I initially hoped for. Maybe after your removals I can look into this again. Thanks, Davidlohr
