On 2/16/21 6:18 PM, Jens Axboe wrote: > On 2/15/21 7:41 PM, Jens Axboe wrote: >> On 2/15/21 3:41 PM, Eric W. Biederman wrote: >>> Jens Axboe <axboe@xxxxxxxxx> writes: >>> >>>> On 2/15/21 11:24 AM, Jens Axboe wrote: >>>>> On 2/15/21 11:07 AM, Eric W. Biederman wrote: >>>>>> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: >>>>>> >>>>>>> On Sun, Feb 14, 2021 at 8:38 AM Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>>>>> >>>>>>>>> Similarly it looks like opening of "/dev/tty" fails to >>>>>>>>> return the tty of the caller but instead fails because >>>>>>>>> io-wq threads don't have a tty. >>>>>>>> >>>>>>>> I've got a patch queued up for 5.12 that clears ->fs and ->files for the >>>>>>>> thread if not explicitly inherited, and I'm working on similarly >>>>>>>> proactively catching these cases that could potentially be problematic. >>>>>>> >>>>>>> Well, the /dev/tty case still needs fixing somehow. >>>>>>> >>>>>>> Opening /dev/tty actually depends on current->signal, and if it is >>>>>>> NULL it will fall back on the first VT console instead (I think). >>>>>>> >>>>>>> I wonder if it should do the same thing /proc/self does.. >>>>>> >>>>>> Would there be any downside of making the io-wq kernel threads be per >>>>>> process instead of per user? >>>>>> >>>>>> I can see a lower probability of a thread already existing. Are there >>>>>> other downsides I am missing? >>>>>> >>>>>> The upside would be that all of the issues of have we copied enough >>>>>> should go away, as the io-wq thread would then behave like another user >>>>>> space thread. To handle posix setresuid() and friends it looks like >>>>>> current_cred would need to be copied but I can't think of anything else. >>>>> >>>>> I really like that idea. Do we currently have a way of creating a thread >>>>> internally, akin to what would happen if the same task did pthread_create? >>>>> That'd ensure that we have everything we need, without actively needing to >>>>> map the request types, or find future issues of "we also need this bit". >>>>> It'd work fine for the 'need new worker' case too, if one goes to sleep. >>>>> We'd just 'fork' off that child. >>>>> >>>>> Would require some restructuring of io-wq, but at the end of it, it'd >>>>> be a simpler solution. >>>> >>>> I was intrigued enough that I tried to wire this up. If we can pull this >>>> off, then it would take a great weight off my shoulders as there would >>>> be no more worries on identity. >>>> >>>> Here's a branch that's got a set of patches that actually work, though >>>> it's a bit of a hack in spots. Notes: >>>> >>>> - Forked worker initially crashed, since it's an actual user thread and >>>> bombed on deref of kernel structures. Expectedly. That's what the >>>> horrible kernel_clone_args->io_wq hack is working around for now. >>>> Obviously not the final solution, but helped move things along so >>>> I could actually test this. >>>> >>>> - Shared io-wq helpers need indexing for task, right now this isn't >>>> done. But that's not hard to do. >>>> >>>> - Idle thread reaping isn't done yet, so they persist until the >>>> context goes away. >>>> >>>> - task_work fallback needs a bit of love. Currently we fallback to >>>> the io-wq manager thread for handling that, but a) manager is gone, >>>> and b) the new workers are now threads and go away as well when >>>> the original task goes away. None of the three fallback sites need >>>> task context, so likely solution here is just punt it to system_wq. >>>> Not the hot path, obviously, we're exiting. >>>> >>>> - Personality registration is broken, it's just Good Enough to compile. >>>> >>>> Probably a few more items that escape me right now. As long as you >>>> don't hit the fallback cases, it appears to work fine for me. And >>>> the diffstat is pretty good to: >>>> >>>> fs/io-wq.c | 418 +++++++++++-------------------------- >>>> fs/io-wq.h | 10 +- >>>> fs/io_uring.c | 314 +++------------------------- >>>> fs/proc/self.c | 7 - >>>> fs/proc/thread_self.c | 7 - >>>> include/linux/io_uring.h | 19 -- >>>> include/linux/sched.h | 3 + >>>> include/linux/sched/task.h | 1 + >>>> kernel/fork.c | 2 + >>>> 9 files changed, 161 insertions(+), 620 deletions(-) >>>> >>>> as it gets rid of _all_ the 'grab this or that piece' that we're >>>> tracking. >>>> >>>> WIP series here: >>>> >>>> https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-worker >>> >>> I took a quick look through the code and in general it seems reasonable. >> >> Great, thanks for checking. > > Cleaner series here: > > https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-worker.v2 > > One question, since I'm a bit stumped. The very top most debug patch: > > https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-worker.v2&id=8a422f030b9630d16d5ec1ff97842a265f88485e > > any idea what is going on here? For some reason, it only happens for > the 'manager' thread. That one doesn't do any work by itself, it's just > tasked with forking a new worker, if we need one. Seems to trigger for all cases with a pthread in the app. This reproduces it: #include <stdio.h> #include <pthread.h> #include <unistd.h> #include <liburing.h> static void *fn(void *data) { struct io_uring ring; io_uring_queue_init(1, &ring, 0); sleep(1); return NULL; } int main(int argc, char *argv[]) { pthread_t t; void *ret; pthread_create(&t, NULL, fn, NULL); pthread_join(t, &ret); return 0; } -- Jens Axboe
