On 1/27/20 4:25 PM, Pavel Begunkov wrote: > On 28/01/2020 02:23, Jens Axboe wrote: >> On 1/27/20 4:17 PM, Pavel Begunkov wrote: >>> On 28/01/2020 02:00, Jens Axboe wrote: >>>> On 1/27/20 3:40 PM, Jens Axboe wrote: >>>>> On 1/27/20 2:45 PM, Pavel Begunkov wrote: >>>>>> On 27/01/2020 23:33, Jens Axboe wrote: >>>>>>> On 1/27/20 7:07 AM, Pavel Begunkov wrote: >>>>>>>> On 1/27/2020 4:39 PM, Jens Axboe wrote: >>>>>>>>> On 1/27/20 6:29 AM, Pavel Begunkov wrote: >>>>>>>>>> On 1/26/2020 8:00 PM, Jens Axboe wrote: >>>>>>>>>>> On 1/26/20 8:11 AM, Pavel Begunkov wrote: >>>>>>>>>>>> On 1/26/2020 4:51 AM, Daurnimator wrote: >>>>>>>>>>>>> On Fri, 24 Jan 2020 at 10:16, Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>>>>>>> Ok. I can't promise it'll play handy for sharing. Though, you'll be out >>>>>>>>>> of space in struct io_uring_params soon anyway. >>>>>>>>> >>>>>>>>> I'm going to keep what we have for now, as I'm really not imagining a >>>>>>>>> lot more sharing - what else would we share? So let's not over-design >>>>>>>>> anything. >>>>>>>>> >>>>>>>> Fair enough. I prefer a ptr to an extendable struct, that will take the >>>>>>>> last u64, when needed. >>>>>>>> >>>>>>>> However, it's still better to share through file descriptors. It's just >>>>>>>> not secure enough the way it's now. >>>>>>> >>>>>>> Is the file descriptor value really a good choice? We just had some >>>>>>> confusion on ring sharing across forks. Not sure using an fd value >>>>>>> is a sane "key" to use across processes. >>>>>>> >>>>>> As I see it, the problem with @mm is that uring is dead-bound to it. >>>>>> For example, a process can create and send uring (e.g. via socket), >>>>>> and then be killed. And that basically means >>>>>> 1. @mm of the process is locked just because of the sent uring >>>>>> instance. >>>>>> 2. a process may have an io_uring, which bound to @mm of another >>>>>> process, even though the layouts may be completely different. >>>>>> >>>>>> File descriptors are different here, because io_uring doesn't know >>>>>> about them, They are controlled by the userspace (send, dup, fork, >>>>>> etc), and don't sabotage all isolation work done in the kernel. A dire >>>>>> example here is stealing io-wq from within a container, which is >>>>>> trivial with global self-made id. I would love to hear, if I am >>>>>> mistaken somewhere. >>>>>> >>>>>> Is there some better option? >>>>> >>>>> OK, so how about this: >>>>> >>>>> - We use the 'fd' as the lookup key. This makes it easy since we can >>>>> just check if it's a io_uring instance or not, we don't need to do any >>>>> tracking on the side. It also means that the application asking for >>>>> sharing must already have some relationship to the process that >>>>> created the ring. >>> >>> Yeah, that's exactly the point. >>> >>>>> >>>>> - mm/creds must be transferred through the work item. Any SQE done on >>>>> behalf of io_uring_enter() directly already has that, if punted we >>>>> must pass the creds and mm. This means we break the static setup of >>>>> io_wq->mm/creds. It also means that we probably have to add that to >>>>> io_wq_work, which kind of sucks, but... >>> >>> ehh, juggling mm's... But don't have anything nicer myself. >> >> We already do juggle mm's, this is no different. A worker potentially >> retain the mm across works if they are the same. >> >>>> It'd fix Stefan's worry too. >>>> >>>>> I think with that we have a decent setup, that's also safe. I've dropped >>>>> the sharing patches for now, from the 5.6 tree. >>>> >>>> So one concern might be SQPOLL, it'll have to use the ctx creds and mm >>>> as usual. I guess that is ok. >>>> >>> >>> OK. I'll send the patches for the first part now, and take a look at >>> the second one a bit latter if isn't done until then. >> >> Hang on a second, I'm doing the mm and creds bits right now. I'll push >> that to a branch, if you want to do the actual fd stuff on top of that, >> that would be great. >> > Sure, should be trivially mergeable. https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-wq Top patch there is the mm/creds passing. I kind of like it even if it means we're growing io_wq_worker (and subsequently io_kiocb) by 16 bytes, as it means we can be more flexible. This solves it for this use case, but also the case that Stefan was worried about. If you respin the last patch I had but using the fd instead, then I think we're in business. -- Jens Axboe
