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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9CF1C433EF for ; Thu, 9 Jun 2022 16:08:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234159AbiFIQIO (ORCPT ); Thu, 9 Jun 2022 12:08:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232457AbiFIQIN (ORCPT ); Thu, 9 Jun 2022 12:08:13 -0400 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 50D79237941 for ; Thu, 9 Jun 2022 09:08:12 -0700 (PDT) Message-ID: <82993fe0-9a38-d87b-5eb3-32dc33464d43@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1654790890; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Y03lUD8h1u65VEyCtCt2pE3sZdRUnZQwmWzZrOKUxnw=; b=BptYAHYuWz/pBAXWVSleZIAe5uPCW/rnuFtbVvgUvC9h5bn5QWpZidPOmhKeSPJ7OLFXKO JpD/NbN6FVhg3u2+pXIAm/Q+fCd2IiisPzPV50gKReLrrL0iXoLOsKxzsf2CU6l6TpXJTk 5v/I7MTFuVJKjUNSNVgyoUu/TxkZxhw= Date: Fri, 10 Jun 2022 00:08:01 +0800 MIME-Version: 1.0 Subject: Re: Possible bug for ring-mapped provided buffer Content-Language: en-US To: Jens Axboe , io-uring Cc: Pavel Begunkov References: <1884ea45-07df-303a-c22c-319a2394b20f@linux.dev> <7c563209-7b33-4cc8-86d9-fecfef68c274@kernel.dk> <8ec6116d-39cd-ed6c-3477-9165d1a27128@kernel.dk> <78e3cf67-a3f2-0ca3-4b83-27aa738c3b20@kernel.dk> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Xu In-Reply-To: <78e3cf67-a3f2-0ca3-4b83-27aa738c3b20@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 6/9/22 23:06, Jens Axboe wrote: > On 6/9/22 4:32 AM, Hao Xu wrote: >> On 6/9/22 18:19, Jens Axboe wrote: >>> On 6/9/22 4:14 AM, Hao Xu wrote: >>>> On 6/9/22 18:06, Jens Axboe wrote: >>>>> On 6/9/22 1:53 AM, Hao Xu wrote: >>>>>> Hi all, >>>>>> I haven't done tests to demonstrate it. It is for partial io case, we >>>>>> don't consume/release the buffer before arm_poll in ring-mapped mode. >>>>>> But seems we should? Otherwise ring head isn't moved and other requests >>>>>> may take that buffer. What do I miss? >>>>> >>>>> On vacation this week, so can't take a look at the code. But the >>>>> principle is precisely not to consume the buffer if we arm poll, because >>>>> then the next one can grab it instead. We don't want to consume a buffer >>>>> over poll, as that defeats the purpose of a provided buffer. It should >>>>> be grabbed and consumed only if we can use it right now. >>>>> >>>>> Hence the way it should work is that we DON'T consume the buffer in this >>>>> case, and that someone else can just use it. At the same time, we should >>>>> ensure that we grab a NEW buffer for this case, whenever the poll >>>> >>>> If we grab a new buffer for it, then we have to copy the data since we >>>> have done partial io...this also defeats the purpose of this feature. >>> >>> For partial IO, we never drop the buffer. See the logic in >>> io_kbuf_recycle(). It should be as follows: >> >> Yea, in io_kbuf_recycle(), if it's partial io, we just return. For >> legacy mode, this means we keep the buffer. For ring-mapped mode, this >> means we then release the uring_lock without moving the ring->head, >> and then other requests may take that buffer which is in use.. >> And next time we do (for example) recv(), we lost the data which we got >> at the previous time. >> Do I miss something? > > If we don't commit for ring mapped buffers, then yeah that's definitely > a bug. Please send a fix :-) > > Pavel can take care of it this week. > I'll send a patch tomorrow. Thanks, Hao