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. Can the io_uring_task_cancel in begin_new_exec go away as well? Today it happens after de_thread and so presumably all of the io_uring threads are already gone. Eric
