On 11/20/20 5:23 PM, Linus Torvalds wrote: > On Fri, Nov 20, 2020 at 1:36 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >> >> I don't disagree with you on that. I've been a bit gun shy on touching >> the VFS side of things, but this one isn't too bad. I hacked up a patch >> that allows io_uring to do LOOKUP_RCU and a quick test seems to indicate >> it's fine. On top of that, we just propagate the error if we do fail and >> get rid of that odd retry loop. > > Ok, this looks better to me (but is obviously not 5.10 material). > > That said, I think I'd prefer to keep 'struct nameidata' internal to > just fs/namei.c, and maybe we can just expert that > > struct nameidata nd; > > set_nameidata(&nd, req->open.dfd, req->open.filename); > file = path_openat(&nd, &op, op.lookup_flags | LOOKUP_RCU); > restore_nameidata(); > return filp == ERR_PTR(-ECHILD) ? -EAGAIN : filp; > > as a helper from namei.c instead? Call it "do_filp_open_rcu()" or something? Yes, that's probably a better idea. I'll move in that direction. > That "force_nonblock" test seems a bit off, though. Why is that RCU > case only done when "!force_nonblock"? It would seem that if > force_nonblock is set, you want to do this too? Taking a second look at it, it's inverted. So if force_nonblock == true, we want to do just the RCU lookup. But I think the bit that you're missing is that the other case will do the normal lookup, which does an RCU lookup first. It looks needs to look like this: if (force_nonblock) file = do_filp_open_rcu(); else file = do_filp_open(); -- Jens Axboe
