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Date: Fri, 20 Nov 2020 16:23:41 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk> Cc: io-uring <io-uring@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [GIT PULL] io_uring fixes for 5.10-rc On Fri, Nov 20, 2020 at 1:36 PM Jens Axboe <axboe@...nel.dk> 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? 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? Al? You can see the background on lkml, but basically io_uring wants to punt file open to a kernel thread, except if it can just be done directly without blocking (which is pretty much that RCU lookup case). And the thing that triggered this is that /proc/self/ can only be done directly - not in a kernel thread. So the RCU case actually ends up being interesting in that it would handl those things. Linus
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