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=-17.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,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 6FDDCC433DB for ; Wed, 23 Dec 2020 02:14:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40F63221E5 for ; Wed, 23 Dec 2020 02:14:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726069AbgLWCOd (ORCPT ); Tue, 22 Dec 2020 21:14:33 -0500 Received: from out30-44.freemail.mail.aliyun.com ([115.124.30.44]:54437 "EHLO out30-44.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725300AbgLWCOd (ORCPT ); Tue, 22 Dec 2020 21:14:33 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R581e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=xiaoguang.wang@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UJUdFTJ_1608689629; Received: from 30.225.32.217(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0UJUdFTJ_1608689629) by smtp.aliyun-inc.com(127.0.0.1); Wed, 23 Dec 2020 10:13:49 +0800 Subject: Re: [PATCH] io_uring: hold uring_lock to complete faild polled io in io_wq_submit_work() To: Jens Axboe , Pavel Begunkov , io-uring@vger.kernel.org Cc: joseph.qi@linux.alibaba.com References: <20201214154941.10907-1-xiaoguang.wang@linux.alibaba.com> <27952c41-111c-b505-e7f1-78b299f4b786@gmail.com> <78388381-c8cf-a024-457d-1ad31207d2ef@kernel.dk> From: Xiaoguang Wang Message-ID: Date: Wed, 23 Dec 2020 10:12:05 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <78388381-c8cf-a024-457d-1ad31207d2ef@kernel.dk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org hi, > On 12/20/20 12:36 PM, Pavel Begunkov wrote: >> On 20/12/2020 19:34, Pavel Begunkov wrote: >>> On 14/12/2020 15:49, Xiaoguang Wang wrote: >>>> io_iopoll_complete() does not hold completion_lock to complete polled >>>> io, so in io_wq_submit_work(), we can not call io_req_complete() directly, >>>> to complete polled io, otherwise there maybe concurrent access to cqring, >>>> defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always >>>> let io_iopoll_complete() complete polled io") has fixed this issue, but >>>> Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests( >>>> IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is >>>> not good. >>>> >>>> Given that io_iopoll_complete() is always called under uring_lock, so here >>>> for polled io, we can also get uring_lock to fix this issue. >>> >>> This returns it to the state it was before fixing + mutex locking for >>> IOPOLL, and it's much better than having it half-broken as it is now. >> >> btw, comments are over 80, but that's minor. > > I fixed that up, but I don't particularly like how 'req' is used after > calling complete. How about the below variant - same as before, just > using the ctx instead to determine if we need to lock it or not. It looks better, thanks. Regards, Xiaoguang Wang > > > commit 253b60e7d8adcb980be91f77e64968a58d836b5e > Author: Xiaoguang Wang > Date: Mon Dec 14 23:49:41 2020 +0800 > > io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work() > > io_iopoll_complete() does not hold completion_lock to complete polled io, > so in io_wq_submit_work(), we can not call io_req_complete() directly, to > complete polled io, otherwise there maybe concurrent access to cqring, > defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always > let io_iopoll_complete() complete polled io") has fixed this issue, but > Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests( > IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is not > good. > > Given that io_iopoll_complete() is always called under uring_lock, so here > for polled io, we can also get uring_lock to fix this issue. > > Fixes: dad1b1242fd5 ("io_uring: always let io_iopoll_complete() complete polled io") > Cc: # 5.5+ > Signed-off-by: Xiaoguang Wang > Reviewed-by: Pavel Begunkov > [axboe: don't deref 'req' after completing it'] > Signed-off-by: Jens Axboe > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index b27f61e3e0d6..0a8cf3fad955 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -6332,19 +6332,28 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work) > } > > if (ret) { > + struct io_ring_ctx *lock_ctx = NULL; > + > + if (req->ctx->flags & IORING_SETUP_IOPOLL) > + lock_ctx = req->ctx; > + > /* > - * io_iopoll_complete() does not hold completion_lock to complete > - * polled io, so here for polled io, just mark it done and still let > - * io_iopoll_complete() complete it. > + * io_iopoll_complete() does not hold completion_lock to > + * complete polled io, so here for polled io, we can not call > + * io_req_complete() directly, otherwise there maybe concurrent > + * access to cqring, defer_list, etc, which is not safe. Given > + * that io_iopoll_complete() is always called under uring_lock, > + * so here for polled io, we also get uring_lock to complete > + * it. > */ > - if (req->ctx->flags & IORING_SETUP_IOPOLL) { > - struct kiocb *kiocb = &req->rw.kiocb; > + if (lock_ctx) > + mutex_lock(&lock_ctx->uring_lock); > > - kiocb_done(kiocb, ret, NULL); > - } else { > - req_set_fail_links(req); > - io_req_complete(req, ret); > - } > + req_set_fail_links(req); > + io_req_complete(req, ret); > + > + if (lock_ctx) > + mutex_unlock(&lock_ctx->uring_lock); > } > > return io_steal_work(req); >