On 8/18/20 7:53 AM, Jens Axboe wrote: > On 8/18/20 7:49 AM, Anoop C S wrote: >> On Tue, 2020-08-18 at 07:44 -0700, Jens Axboe wrote: >>> On 8/18/20 12:40 AM, Stefan Metzmacher wrote: >>>> Hi Jens, >>>> >>>>>>>> Will this be backported? >>>>>>> >>>>>>> I can, but not really in an efficient manner. It depends on >>>>>>> the async >>>>>>> buffered work to make progress, and the task_work handling >>>>>>> retry. The >>>>>>> latter means it's 5.7+, while the former is only in 5.9+... >>>>>>> >>>>>>> We can make it work for earlier kernels by just using the >>>>>>> thread offload >>>>>>> for that, and that may be worth doing. That would enable it >>>>>>> in >>>>>>> 5.7-stable and 5.8-stable. For that, you just need these two >>>>>>> patches. >>>>>>> Patch 1 would work as-is, while patch 2 would need a small >>>>>>> bit of >>>>>>> massaging since io_read() doesn't have the retry parts. >>>>>>> >>>>>>> I'll give it a whirl just out of curiosity, then we can >>>>>>> debate it after >>>>>>> that. >>>>>> >>>>>> Here are the two patches against latest 5.7-stable (the rc >>>>>> branch, as >>>>>> we had quite a few queued up after 5.9-rc1). Totally untested, >>>>>> just >>>>>> wanted to see if it was doable. >>>>>> >>>>>> First patch is mostly just applied, with various bits removed >>>>>> that we >>>>>> don't have in 5.7. The second patch just does -EAGAIN punt for >>>>>> the >>>>>> short read case, which will queue the remainder with io-wq for >>>>>> async execution. >>>>>> >>>>>> Obviously needs quite a bit of testing before it can go >>>>>> anywhere else, >>>>>> but wanted to throw this out there in case you were interested >>>>>> in >>>>>> giving it a go... >>>>> >>>>> Actually passes basic testing, and doesn't return short reads. So >>>>> at >>>>> least it's not half bad, and it should be safe for you to test. >>>>> >>>>> I quickly looked at 5.8 as well, and the good news is that the >>>>> same >>>>> patches will apply there without changes. >>>> >>>> Thanks, but I was just curios and I currently don't have the >>>> environment to test, sorry. >>>> >>>> Anoop: you helped a lot reproducing the problem with 5.6, would you >>>> be able to >>>> test the kernel patches against 5.7 or 5.8, while reverting the >>>> samba patches? >>>> See >>>> https://lore.kernel.org/io-uring/e22220a8-669a-d302-f454-03a35c9582b4@xxxxxxxxx/T/#t >>>> for the >>>> whole discussion? >>> >>> I'm actually not too worried about the short reads not working, it'll >>> naturally fall out correctly if the rest of the path is sane. The >>> latter >>> is what I'd be worried about! I ran some synthetic testing and >>> haven't >>> seen any issues so far, so maybe (just maybe) it's actually good. >>> >>> I can setup two branches with the 5.7-stable + patches and 5.8-stable >>> + >>> patches if that helps facilitate testing? >> >> That would be great. >> >> I took those two patches and tried to apply on top of 5.7.y. I had to >> manually resolve very few conflicts. I am not sure whether it is OK or >> not to test such a patched version(because of conflicts). > > I pushed out two branches: > > 5.8-stable: current 5.8-stable rc queue + the three patches for this > 5.7-stable: 5.7 ditto > > So pick which one you want to use, and then pull it. > > git://git.kernel.dk/linux-block 5.8-stable > > git://git.kernel.dk/linux-block 5.7-stable > > Hope that helps! Ran these through the liburing regression testing as well, and found a case where 'ret2' isn't initialized. So pushed out new branches. The correct sha for testing should be: 5.7-stable: a451911d530075352fbc7ef9bb2df68145a747ad 5.8-stable: b101e651782a60eb1e96b64e523e51358b77f94f -- Jens Axboe
