From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13CE5C432BE for ; Fri, 23 Jul 2021 17:15:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9B9A60ED4 for ; Fri, 23 Jul 2021 17:15:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230126AbhGWQfL (ORCPT ); Fri, 23 Jul 2021 12:35:11 -0400 Received: from zeniv-ca.linux.org.uk ([142.44.231.140]:48686 "EHLO zeniv-ca.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229492AbhGWQfL (ORCPT ); Fri, 23 Jul 2021 12:35:11 -0400 Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m6yhl-003E8O-EE; Fri, 23 Jul 2021 17:11:21 +0000 Date: Fri, 23 Jul 2021 17:11:21 +0000 From: Al Viro To: Jens Axboe Cc: Pavel Begunkov , io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH 3/3] io_uring: refactor io_sq_offload_create() Message-ID: References: <939776f90de8d2cdd0414e1baa29c8ec0926b561.1618916549.git.asml.silence@gmail.com> <57758edf-d064-d37e-e544-e0c72299823d@kernel.dk> <8fb39022-ba21-2c1f-3df5-29be002014d8@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8fb39022-ba21-2c1f-3df5-29be002014d8@kernel.dk> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Jul 23, 2021 at 10:17:27AM -0600, Jens Axboe wrote: > On 7/22/21 6:10 PM, Al Viro wrote: > > On Thu, Jul 22, 2021 at 05:42:55PM -0600, Jens Axboe wrote: > > > >>> So how can we possibly get there with tsk->files == NULL and what does it > >>> have to do with files, anyway? > >> > >> It's not the clearest, but the files check is just to distinguish between > >> exec vs normal cancel. For exec, we pass in files == NULL. It's not > >> related to task->files being NULL or not, we explicitly pass NULL for > >> exec. > > > > Er... So turn that argument into bool cancel_all, and pass false on exit and > > true on exec? > > Yes > > > While we are at it, what happens if you pass io_uring descriptor > > to another process, close yours and then have the recepient close the one it > > has gotten? AFAICS, io_ring_ctx_wait_and_kill(ctx) will be called in context > > of a process that has never done anything io_uring-related. Can it end up > > trying to resubmit some requests?> > > I rather hope it can't happen, but I don't see what would prevent it... > > No, the pending request would either have gone to a created thread of > the original task on submission, or it would be sitting in a > ready-to-retry state. The retry would attempt to queue to original task, > and either succeed (if still alive) or get failed with -ECANCELED. Any > given request is tied to the original task. Hmm... Sure, you'll be pushing it to the same io_wqe it went through originally, but you are still in context of io_uring_release() caller, aren't you? So you call io_wqe_wake_worker(), and it decides that all threads are busy, but ->nr_workers is still below ->max_workers. And proceeds to create_io_worker(wqe->wq, wqe, acct->index); which will create a new io-worker thread, but do that in the thread group of current, i.e. the caller of io_uring_release(). Looks like we'd get an io-worker thread with the wrong parent... What am I missing here?