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. -- Jens Axboe
