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=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 898C5C433DF for ; Sat, 4 Jul 2020 02:08:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 566C92070B for ; Sat, 4 Jul 2020 02:08:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="Axd1Ghe7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726554AbgGDCIU (ORCPT ); Fri, 3 Jul 2020 22:08:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726469AbgGDCIU (ORCPT ); Fri, 3 Jul 2020 22:08:20 -0400 Received: from mail-pg1-x542.google.com (mail-pg1-x542.google.com [IPv6:2607:f8b0:4864:20::542]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68B4DC061794 for ; Fri, 3 Jul 2020 19:08:20 -0700 (PDT) Received: by mail-pg1-x542.google.com with SMTP id g67so14932384pgc.8 for ; Fri, 03 Jul 2020 19:08:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:references:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=rZsG7WRF35sRAUGahw36hRb0//zdeBlcNkLR8sY8tcY=; b=Axd1Ghe7XStzNeCgkJYDZx/ty12xKmoWmLxFEYhpsV5qF5H36TJFi5mi6ifzyH++dw e2OtGujyBUOxAUMezHpXVSFZW+E4yPoJ+QvgakUOtkxltZoz93t+IEvKLO3G4TNvQuti b876ZYi1ZTZYHb5WPznsO24KncF9HtvOQXjh7AbaEwyYW/pRdTw4bsTnZhxaWAwqE+Mw CCwf2W2e6gPoAAA0vswAbP9xi6nu/rawBwrKVcz5CnMZDAmxk9/CjoKRtugTfbb1NI4S Uz0layVbJ0ur5u7XluqMt2eh575TVV1e3IcinzKtge/bz4cA/Z7vOzuwxC9bhaHPn0ln 6krg== 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:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=rZsG7WRF35sRAUGahw36hRb0//zdeBlcNkLR8sY8tcY=; b=R/pLt0Ug8j4HS6XUgReDYqzgOxsr4b6wpPAF9mjXI1q7MFeN4jWByHQDjpO+mtYsaK vwtKKPTWsAtBBmBUeS8qTOfSynrtlJla7AW17razBBsqTRol1mMPBefXbVX+K+TZKXcV pDCU9xniIxpFqjtHTOZDR4VERtfyfzWKmV/KGPMa/u+jbYbKDTwFrrTnMPTbRqHB6FLb C50Hcr+5BaMiAsTp7l0HqgkOrC3Pw5aSBzQuDtqr9dA/8ZtOUoaPwyf0mz2cpQFXzOPa b7P6JZoKzSe6Moa/HDG4miLFRs/he1So/xK5c881USvPP9YbitBLaLY60Z1ZV64OiC+W XUGQ== X-Gm-Message-State: AOAM5335lTZ1PLXarfslt5b26nmPaQUFTeiCWXQu94gSAS61avL8YdZG qC+OWO+8WccJuGZW6kaEScL7L9TBXzoV9g== X-Google-Smtp-Source: ABdhPJxH8+yuHFDY9I2DrFxMKL5MTShIq/Rkows783owp5LmC9AuVKPv+QjOODZKDwDI9PHGYK8qRw== X-Received: by 2002:aa7:8555:: with SMTP id y21mr19327305pfn.75.1593828499631; Fri, 03 Jul 2020 19:08:19 -0700 (PDT) Received: from [192.168.1.182] ([66.219.217.173]) by smtp.gmail.com with ESMTPSA id j36sm13307673pgj.39.2020.07.03.19.08.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Jul 2020 19:08:18 -0700 (PDT) Subject: Re: signals not reliably interrupting io_uring_enter anymore From: Jens Axboe To: Andres Freund , io-uring@vger.kernel.org References: <20200704000049.3elr2mralckeqmej@alap3.anarazel.de> <20200704001541.6isrwsr6ptvbykdq@alap3.anarazel.de> <70fb9308-2126-052b-730a-bc5adad552f9@kernel.dk> <7C9DC2D8-6FF5-477D-B539-3A9F5DE1B13B@anarazel.de> Message-ID: Date: Fri, 3 Jul 2020 20:08:17 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 7/3/20 7:52 PM, Jens Axboe wrote: > On 7/3/20 7:13 PM, Andres Freund wrote: >> Hi, >> >> On July 3, 2020 5:48:21 PM PDT, Jens Axboe wrote: >>> On 7/3/20 6:15 PM, Andres Freund wrote: >>>> Hi, >>>> >>>> On 2020-07-03 17:00:49 -0700, Andres Freund wrote: >>>>> I haven't yet fully analyzed the problem, but after updating to >>>>> cdd3bb54332f82295ed90cd0c09c78cd0c0ee822 io_uring using postgres >>> does >>>>> not work reliably anymore. >>>>> >>>>> The symptom is that io_uring_enter(IORING_ENTER_GETEVENTS) isn't >>>>> interrupted by signals anymore. The signal handler executes, but >>>>> afterwards the syscall is restarted. Previously io_uring_enter >>> reliably >>>>> returned EINTR in that case. >>>>> >>>>> Currently postgres relies on signals interrupting io_uring_enter(). >>> We >>>>> probably can find a way to not do so, but it'd not be entirely >>> trivial. >>>>> >>>>> I suspect the issue is >>>>> >>>>> commit ce593a6c480a22acba08795be313c0c6d49dd35d (tag: >>> io_uring-5.8-2020-07-01, linux-block/io_uring-5.8) >>>>> Author: Jens Axboe >>>>> Date: 2020-06-30 12:39:05 -0600 >>>>> >>>>> io_uring: use signal based task_work running >>>>> >>>>> as that appears to have changed the error returned by >>>>> io_uring_enter(GETEVENTS) after having been interrupted by a signal >>> from >>>>> EINTR to ERESTARTSYS. >>>>> >>>>> >>>>> I'll check to make sure that the issue doesn't exist before the >>> above >>>>> commit. >>>> >>>> Indeed, on cd77006e01b3198c75fb7819b3d0ff89709539bb the PG issue >>> doesn't >>>> exist, which pretty much confirms that the above commit is the issue. >>>> >>>> What was the reason for changing EINTR to ERESTARTSYS in the above >>>> commit? I assume trying to avoid returning spurious EINTRs to >>> userland? >>> >>> Yeah, for when it's running task_work. I wonder if something like the >>> below will do the trick? >>> >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 700644a016a7..0efa73d78451 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -6197,11 +6197,11 @@ static int io_cqring_wait(struct io_ring_ctx >>> *ctx, int min_events, >>> do { >>> prepare_to_wait_exclusive(&ctx->wait, &iowq.wq, >>> TASK_INTERRUPTIBLE); >>> - /* make sure we run task_work before checking for signals */ >>> - if (current->task_works) >>> - task_work_run(); >>> if (signal_pending(current)) { >>> - ret = -ERESTARTSYS; >>> + if (current->task_works) >>> + ret = -ERESTARTSYS; >>> + else >>> + ret = -EINTR; >>> break; >>> } >>> if (io_should_wake(&iowq, false)) >>> @@ -6210,7 +6210,7 @@ static int io_cqring_wait(struct io_ring_ctx >>> *ctx, int min_events, >>> } while (1); >>> finish_wait(&ctx->wait, &iowq.wq); >>> >>> - restore_saved_sigmask_unless(ret == -ERESTARTSYS); >>> + restore_saved_sigmask_unless(ret == -EINTR); >>> >>> return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : >>> 0; >>> } >> >> I'll try in a bit. Suspect however that there'd be trouble if there >> were both an actual signal and task work pending? > > Yes, I have that worry too. We'd really need to check if we have an > actual signal pending - if we do, we still do -EINTR. If not, then we > just do -ERESTARTSYS and restart the system call after task_work has > been completed. Half-assed approach below, I suspect this won't _really_ > work without appropriate locking. Which would be unfortunate. > > Either that, or we'd need to know if an actual signal was delivered when > we get re-entered due to returning -ERESTARTSYS. If it was just > task_work being run, then we're fine. But if an actual signal was > pending, then we'd need to return -EINTR. > > CC'ing Oleg to see if he has any good ideas here. This might be simpler: diff --git a/fs/io_uring.c b/fs/io_uring.c index 700644a016a7..8f54fd5085bf 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6197,11 +6197,11 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, do { prepare_to_wait_exclusive(&ctx->wait, &iowq.wq, TASK_INTERRUPTIBLE); - /* make sure we run task_work before checking for signals */ - if (current->task_works) - task_work_run(); if (signal_pending(current)) { - ret = -ERESTARTSYS; + if (!sigisemptyset(¤t->pending.signal)) + ret = -EINTR; + else + ret = -ERESTARTSYS; break; } if (io_should_wake(&iowq, false)) @@ -6210,7 +6210,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, } while (1); finish_wait(&ctx->wait, &iowq.wq); - restore_saved_sigmask_unless(ret == -ERESTARTSYS); + restore_saved_sigmask_unless(ret == -EINTR); return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0; } -- Jens Axboe