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=-10.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 554F5C433E0 for ; Wed, 17 Feb 2021 03:12:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 071B064DFF for ; Wed, 17 Feb 2021 03:12:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229684AbhBQDMU (ORCPT ); Tue, 16 Feb 2021 22:12:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45356 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229623AbhBQDMR (ORCPT ); Tue, 16 Feb 2021 22:12:17 -0500 Received: from mail-pg1-x52d.google.com (mail-pg1-x52d.google.com [IPv6:2607:f8b0:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 730D5C061574 for ; Tue, 16 Feb 2021 19:11:37 -0800 (PST) Received: by mail-pg1-x52d.google.com with SMTP id b21so7606758pgk.7 for ; Tue, 16 Feb 2021 19:11:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=4utzFdmE/sMU637scLRb8aqgr5WIQGeIEUnlpvA+fVE=; b=jL6kr8T2tsLR6aeTV0vFYQxgfGXHXK90qWnRdXxZLpW1pFSReTUNy9k+Vq1kZ3a2ha uHWvU15buxx2IM+ZtPmfuSuclmmz6ldalSJn/OTETdENh9QUW8a7KpwbdjWPFesqV/7M A1Pe9W4fbYXFktA3oOW+CfQ0BMonMp6FwDfFd25BHSn+ey+x0upBjC3ghughCupD83nL sjfPKIlXOhr9eAm6lNGBDx9+57wzt5xXhp7uAsKROmLcSURAIAYR8mMTnSK6voRUC7gQ Jy6X/YZQoOSi7YeVuQnHCCdXx+fzdVEwuXFnOlk34fupnBvLZscqQ1g2EIzMUqXmLTkp cIGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=4utzFdmE/sMU637scLRb8aqgr5WIQGeIEUnlpvA+fVE=; b=X5nlumH7YXja9zivhhnrLjSZ6Yt/oua7lP0XtAso/QAxceNG6rGg/t+6pkWAFWcJw3 sLcP+prfvIXc7os1ukQ0EJuao6NUlzzvRSWuexYAU8dM99/xGKJFded8g7Nr21vpTVxD dVvWNVxXMmaK7nfirUUQ7aB+2fYmZV3FxUm/y/TeQ2xj1ZoNa/Bd0x9g8PrxQ5l+JwZS rAwavxT9+/ff5N+ZoHOTBwl83q4un4t24iytksr0xq5tI3Rl9YRQrXLISVd3484fVoXr LLKmD3WoITR8qNGnOsYXzWZ8dy3AoCc74DYZE5+nRpp3Fd4tUHPx9pnYlh4mF6rCwahD G3jQ== X-Gm-Message-State: AOAM532AZKc6OeRDFP7HnMPYhCXYoUVGcnF24mOmPFJDqB6VXfmsTAXP 4MNMfm6o7+ojUQpYDWAPg6IoHw== X-Google-Smtp-Source: ABdhPJylKlCWkV/cu5S0sYm4Ggwi9yf7QBAqq5SWw+GKJ+8vdzzfvtApALWCs4FBTlnekWEszNYPwA== X-Received: by 2002:a63:343:: with SMTP id 64mr22238705pgd.232.1613531496808; Tue, 16 Feb 2021 19:11:36 -0800 (PST) Received: from [192.168.1.134] ([66.219.217.173]) by smtp.gmail.com with ESMTPSA id j1sm319300pjf.26.2021.02.16.19.11.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Feb 2021 19:11:36 -0800 (PST) Subject: Re: [PATCHSET v3 0/4] fs: Support for LOOKUP_NONBLOCK / RESOLVE_NONBLOCK (Insufficiently faking current?) From: Jens Axboe To: "Eric W. Biederman" Cc: Linus Torvalds , linux-fsdevel , Al Viro References: <20201214191323.173773-1-axboe@kernel.dk> <94731b5a-a83e-91b5-bc6c-6fd4aaacb704@kernel.dk> <99b642d3-6a38-af68-b99d-44efcf0b13a5@kernel.dk> <9d9b5143-6b26-49d4-a11a-b21c020d5886@kernel.dk> <86cd3801-dfb4-833a-b7e6-e643186030e7@kernel.dk> Message-ID: <0cdf16a5-3efb-dea0-303c-bbfbe880ca7a@kernel.dk> Date: Tue, 16 Feb 2021 20:11:34 -0700 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: <86cd3801-dfb4-833a-b7e6-e643186030e7@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2/16/21 6:26 PM, Jens Axboe wrote: > On 2/16/21 6:18 PM, Jens Axboe wrote: >> On 2/15/21 7:41 PM, Jens Axboe wrote: >>> On 2/15/21 3:41 PM, Eric W. Biederman wrote: >>>> Jens Axboe writes: >>>> >>>>> On 2/15/21 11:24 AM, Jens Axboe wrote: >>>>>> On 2/15/21 11:07 AM, Eric W. Biederman wrote: >>>>>>> Linus Torvalds writes: >>>>>>> >>>>>>>> On Sun, Feb 14, 2021 at 8:38 AM Jens Axboe wrote: >>>>>>>>> >>>>>>>>>> Similarly it looks like opening of "/dev/tty" fails to >>>>>>>>>> return the tty of the caller but instead fails because >>>>>>>>>> io-wq threads don't have a tty. >>>>>>>>> >>>>>>>>> I've got a patch queued up for 5.12 that clears ->fs and ->files for the >>>>>>>>> thread if not explicitly inherited, and I'm working on similarly >>>>>>>>> proactively catching these cases that could potentially be problematic. >>>>>>>> >>>>>>>> Well, the /dev/tty case still needs fixing somehow. >>>>>>>> >>>>>>>> Opening /dev/tty actually depends on current->signal, and if it is >>>>>>>> NULL it will fall back on the first VT console instead (I think). >>>>>>>> >>>>>>>> I wonder if it should do the same thing /proc/self does.. >>>>>>> >>>>>>> Would there be any downside of making the io-wq kernel threads be per >>>>>>> process instead of per user? >>>>>>> >>>>>>> I can see a lower probability of a thread already existing. Are there >>>>>>> other downsides I am missing? >>>>>>> >>>>>>> The upside would be that all of the issues of have we copied enough >>>>>>> should go away, as the io-wq thread would then behave like another user >>>>>>> space thread. To handle posix setresuid() and friends it looks like >>>>>>> current_cred would need to be copied but I can't think of anything else. >>>>>> >>>>>> I really like that idea. Do we currently have a way of creating a thread >>>>>> internally, akin to what would happen if the same task did pthread_create? >>>>>> That'd ensure that we have everything we need, without actively needing to >>>>>> map the request types, or find future issues of "we also need this bit". >>>>>> It'd work fine for the 'need new worker' case too, if one goes to sleep. >>>>>> We'd just 'fork' off that child. >>>>>> >>>>>> Would require some restructuring of io-wq, but at the end of it, it'd >>>>>> be a simpler solution. >>>>> >>>>> I was intrigued enough that I tried to wire this up. If we can pull this >>>>> off, then it would take a great weight off my shoulders as there would >>>>> be no more worries on identity. >>>>> >>>>> Here's a branch that's got a set of patches that actually work, though >>>>> it's a bit of a hack in spots. Notes: >>>>> >>>>> - Forked worker initially crashed, since it's an actual user thread and >>>>> bombed on deref of kernel structures. Expectedly. That's what the >>>>> horrible kernel_clone_args->io_wq hack is working around for now. >>>>> Obviously not the final solution, but helped move things along so >>>>> I could actually test this. >>>>> >>>>> - Shared io-wq helpers need indexing for task, right now this isn't >>>>> done. But that's not hard to do. >>>>> >>>>> - Idle thread reaping isn't done yet, so they persist until the >>>>> context goes away. >>>>> >>>>> - task_work fallback needs a bit of love. Currently we fallback to >>>>> the io-wq manager thread for handling that, but a) manager is gone, >>>>> and b) the new workers are now threads and go away as well when >>>>> the original task goes away. None of the three fallback sites need >>>>> task context, so likely solution here is just punt it to system_wq. >>>>> Not the hot path, obviously, we're exiting. >>>>> >>>>> - Personality registration is broken, it's just Good Enough to compile. >>>>> >>>>> Probably a few more items that escape me right now. As long as you >>>>> don't hit the fallback cases, it appears to work fine for me. And >>>>> the diffstat is pretty good to: >>>>> >>>>> fs/io-wq.c | 418 +++++++++++-------------------------- >>>>> fs/io-wq.h | 10 +- >>>>> fs/io_uring.c | 314 +++------------------------- >>>>> fs/proc/self.c | 7 - >>>>> fs/proc/thread_self.c | 7 - >>>>> include/linux/io_uring.h | 19 -- >>>>> include/linux/sched.h | 3 + >>>>> include/linux/sched/task.h | 1 + >>>>> kernel/fork.c | 2 + >>>>> 9 files changed, 161 insertions(+), 620 deletions(-) >>>>> >>>>> as it gets rid of _all_ the 'grab this or that piece' that we're >>>>> tracking. >>>>> >>>>> WIP series here: >>>>> >>>>> https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-worker >>>> >>>> I took a quick look through the code and in general it seems reasonable. >>> >>> Great, thanks for checking. >> >> Cleaner series here: >> >> https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-worker.v2 >> >> One question, since I'm a bit stumped. The very top most debug patch: >> >> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-worker.v2&id=8a422f030b9630d16d5ec1ff97842a265f88485e >> >> any idea what is going on here? For some reason, it only happens for >> the 'manager' thread. That one doesn't do any work by itself, it's just >> tasked with forking a new worker, if we need one. > > Seems to trigger for all cases with a pthread in the app. This reproduces > it: Nevermind, it was me being an idiot. I had a case in the manager thread that did return 0 instead of do_exit()... -- Jens Axboe