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! -- Jens Axboe
