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=-5.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9A3C8C4320A for ; Thu, 22 Jul 2021 23:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 808FD60EB6 for ; Thu, 22 Jul 2021 23:43:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232024AbhGVXC0 (ORCPT ); Thu, 22 Jul 2021 19:02:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232676AbhGVXCY (ORCPT ); Thu, 22 Jul 2021 19:02:24 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE3B8C061575 for ; Thu, 22 Jul 2021 16:42:57 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id gx2so8281914pjb.5 for ; Thu, 22 Jul 2021 16:42:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=bkuHWBGkKEe0/2yCu3CYpAcsngktc49mg9N4X5eshww=; b=bi/mem5UEK8uuA+WAZ3f37/Ej4WBRo78trRBGEM1yZdL/fdiKw84SB/i26ZqhBeJql 0OBsVSDvVdvN2OOBSWYOSR3TMCpqZ3KnSpV3nbFD5WPQeKAd8f1tuGXpES9C8gs4yyD1 zo9K4HQcZEbZdZ/JwE/W6b3HBfGJYQYii+Gwjl8vuZtt8F6kLgf0Sw1iJh4lpWtha0Q7 6oExucVtB1CPMpH/iMPRQBLm8CwGUiKJEHKe3zC/+0c2rjQJbUa/jqQQrJkJdE169n5Q Z8sUgNI0p93p9LZTzKE4m4a6FhcUDJ3Wv8aSO0HSQb5KGTHLWRseDGcwDxkGLpZQaKSY eOEg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=bkuHWBGkKEe0/2yCu3CYpAcsngktc49mg9N4X5eshww=; b=fJjfQmIxL3tp6ZXIi0mqKchurkT09wI+w2OkLAEP9QAfhw8xG/Rjp10YWJZYUOpdME EzPbe5+DQE27O3JmnWTX+0xUUOw45ZONSgk5PbwzS6HJE9GQOjFR3UW4YsvJ5vRn9dNG s5dxmkieqejrilV4ComXlqE6QmNsymw6i+OygSqSHJAJYTgIMkN5X4VMKg3dr2Y/Xxie 6h+04ZJMe7bq7oYG9G4WXHU+DgKdJPXMhCp9VIJpiH3pK8dR38K3MxUlLMZGUs4MW1iy 7RrvY2awiruudPZIXJ/doZCKJJkRY5Jl3JFT45rGsY33TVF0/ADA1RUOwP8wca05PGig RPvQ== X-Gm-Message-State: AOAM530N04srQnyn3/J+inbRyKMPEtf+2O9+LUOO3fLYasObWirg+AyJ CDavghDsmoVwUsr05fGqD2jYig== X-Google-Smtp-Source: ABdhPJxKpS1tFgoUnKVV34+0WI7GszJldxT7QKj4Ob5J/Z9ejlybBlXIKfSyYBJ3287AejdsrOLlpw== X-Received: by 2002:a63:1d18:: with SMTP id d24mr2295691pgd.69.1626997377261; Thu, 22 Jul 2021 16:42:57 -0700 (PDT) Received: from [192.168.1.187] ([198.8.77.61]) by smtp.gmail.com with ESMTPSA id a13sm32977826pfl.92.2021.07.22.16.42.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Jul 2021 16:42:56 -0700 (PDT) Subject: Re: [PATCH 3/3] io_uring: refactor io_sq_offload_create() To: Al Viro Cc: Pavel Begunkov , io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, Linus Torvalds References: <939776f90de8d2cdd0414e1baa29c8ec0926b561.1618916549.git.asml.silence@gmail.com> <57758edf-d064-d37e-e544-e0c72299823d@kernel.dk> From: Jens Axboe Message-ID: Date: Thu, 22 Jul 2021 17:42:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 7/22/21 5:30 PM, Al Viro wrote: > On Thu, Jul 22, 2021 at 05:06:24PM -0600, Jens Axboe wrote: > >> But yes, that is not great and obviously a bug, and we'll of course get >> it fixed up asap. > > Another fun question: in do_exit() you have > io_uring_files_cancel(tsk->files); > > with > > static inline void io_uring_files_cancel(struct files_struct *files) > { > if (current->io_uring) > __io_uring_cancel(files); > } > > and > > void __io_uring_cancel(struct files_struct *files) > { > io_uring_cancel_generic(!files, NULL); > } > > What the hell is that about? What are you trying to check there? > > All assignments to ->files: > init/init_task.c:116: .files = &init_files, > Not NULL. > fs/file.c:433: tsk->files = NULL; > exit_files(), sets to NULL > fs/file.c:741: me->files = cur_fds; > __close_range(), if the value has been changed at all, the new one > came from if (fds) swap(cur_fds, fds), so it can't become NULL here. > kernel/fork.c:1482: tsk->files = newf; > copy_files(), immediately preceded by verifying newf != NULL > kernel/fork.c:3044: current->files = new_fd; > ksys_unshare(), under if (new_fd) > kernel/fork.c:3097: task->files = copy; > unshare_files(), with if (error || !copy) return error; > slightly upstream. > > IOW, task->files can be NULL *ONLY* after exit_files(). There are two callers > of that; one is for stillborns in copy_process(), another - in do_exit(), > well past that call of io_uring_files_cancel(). And around that call we have > > if (unlikely(tsk->flags & PF_EXITING)) { > pr_alert("Fixing recursive fault but reboot is needed!\n"); > futex_exit_recursive(tsk); > set_current_state(TASK_UNINTERRUPTIBLE); > schedule(); > } > io_uring_files_cancel(tsk->files); > exit_signals(tsk); /* sets PF_EXITING */ > > 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. -- Jens Axboe