On 7/25/23 2:51?PM, Linus Torvalds wrote: > On Tue, 25 Jul 2023 at 13:41, Jens Axboe <axboe@xxxxxxxxx> wrote: >> >> Right, but what if the original app closes the file descriptor? Now you >> have the io_uring file table still holding a reference to it, but it'd >> just be 1. Which is enough to keep it alive, but you can still have >> multiple IOs inflight against this file. > > Note that fdget_pos() fundamentally only works on file descriptors > that are there - it's literally looking them up in the file table as > it goes along. And it looks at the count of the file description as it > is looked up. So that refcount is guaranteed to exist. > > If the file has been closed, fdget_pos() will just fail because it > doesn't find it. > > And if it's then closed *afterwards*, that's fine and doesn't affect > anything, because the locking has been done and we saved away the > status bit as FDPUT_POS_UNLOCK, so the code knows to unlock even if > the file descriptor in the meantime has turned back to having just a > single refcount. Ah yes good point. If registered with io_uring and closed, then it won't matter how many extra references we hold or grab in the future, it won't be found in the file table. I guess that's obvious... -- Jens Axboe
