From patchwork Mon Feb 24 07:03:54 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Xiaoguang Wang X-Patchwork-Id: 1242838 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=linux-ext4-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.alibaba.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 48QtNw19x9z9sRQ for ; Mon, 24 Feb 2020 18:05:04 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726925AbgBXHFD (ORCPT ); Mon, 24 Feb 2020 02:05:03 -0500 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:50287 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbgBXHFC (ORCPT ); Mon, 24 Feb 2020 02:05:02 -0500 X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R341e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=e01e04407; MF=xiaoguang.wang@linux.alibaba.com; NM=1; PH=DS; RN=5; SR=0; TI=SMTPD_---0Tqlb7Pz_1582527869; Received: from localhost(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0Tqlb7Pz_1582527869) by smtp.aliyun-inc.com(127.0.0.1); Mon, 24 Feb 2020 15:04:37 +0800 From: Xiaoguang Wang To: io-uring@vger.kernel.org Cc: linux-ext4@vger.kernel.org, axboe@kernel.dk, joseph.qi@linux.alibaba.com, Xiaoguang Wang Subject: [PATCH v3] io_uring: fix poll_list race for SETUP_IOPOLL|SETUP_SQPOLL Date: Mon, 24 Feb 2020 15:03:54 +0800 Message-Id: <20200224070354.3774-1-xiaoguang.wang@linux.alibaba.com> X-Mailer: git-send-email 2.17.2 Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org After making ext4 support iopoll method: let ext4_file_operations's iopoll method be iomap_dio_iopoll(), we found fio can easily hang in fio_ioring_getevents() with below fio job: rm -f testfile; sync; sudo fio -name=fiotest -filename=testfile -iodepth=128 -thread -rw=write -ioengine=io_uring -hipri=1 -sqthread_poll=1 -direct=1 -bs=4k -size=10G -numjobs=8 -runtime=2000 -group_reporting with IORING_SETUP_SQPOLL and IORING_SETUP_IOPOLL enabled. There are two issues that results in this hang, one reason is that when IORING_SETUP_SQPOLL and IORING_SETUP_IOPOLL are enabled, fio does not use io_uring_enter to get completed events, it relies on kernel io_sq_thread to poll for completed events. Another reason is that there is a race: when io_submit_sqes() in io_sq_thread() submits a batch of sqes, variable 'inflight' will record the number of submitted reqs, then io_sq_thread will poll for reqs which have been added to poll_list. But note, if some previous reqs have been punted to io worker, these reqs will won't be in poll_list timely. io_sq_thread() will only poll for a part of previous submitted reqs, and then find poll_list is empty, reset variable 'inflight' to be zero. If app just waits these deferred reqs and does not wake up io_sq_thread again, then hang happens. For app that entirely relies on io_sq_thread to poll completed requests, let io_iopoll_req_issued() wake up io_sq_thread properly when adding new element to poll_list. Fixes: 2b2ed9750fc9 ("io_uring: fix bad inflight accounting for SETUP_IOPOLL|SETUP_SQTHREAD") Signed-off-by: Xiaoguang Wang --- V2: simple code cleanups and add necessary comments. V3: rebase to v5.6-rc3. --- fs/io_uring.c | 72 ++++++++++++++++++++++++++++----------------------- 1 file changed, 40 insertions(+), 32 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index de650df9ac53..91f5d6c6cd95 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1821,6 +1821,9 @@ static void io_iopoll_req_issued(struct io_kiocb *req) list_add(&req->list, &ctx->poll_list); else list_add_tail(&req->list, &ctx->poll_list); + + if (ctx->flags & IORING_SETUP_SQPOLL && wq_has_sleeper(&ctx->sqo_wait)) + wake_up(&ctx->sqo_wait); } static void io_file_put(struct io_submit_state *state) @@ -5081,9 +5084,9 @@ static int io_sq_thread(void *data) const struct cred *old_cred; mm_segment_t old_fs; DEFINE_WAIT(wait); - unsigned inflight; unsigned long timeout; - int ret; + int ret = 0; + bool needs_uring_lock = false; complete(&ctx->completions[1]); @@ -5091,39 +5094,21 @@ static int io_sq_thread(void *data) set_fs(USER_DS); old_cred = override_creds(ctx->creds); - ret = timeout = inflight = 0; + if (ctx->flags & IORING_SETUP_IOPOLL) + needs_uring_lock = true; + timeout = jiffies + ctx->sq_thread_idle; while (!kthread_should_park()) { unsigned int to_submit; - if (inflight) { + if (!list_empty(&ctx->poll_list)) { unsigned nr_events = 0; - if (ctx->flags & IORING_SETUP_IOPOLL) { - /* - * inflight is the count of the maximum possible - * entries we submitted, but it can be smaller - * if we dropped some of them. If we don't have - * poll entries available, then we know that we - * have nothing left to poll for. Reset the - * inflight count to zero in that case. - */ - mutex_lock(&ctx->uring_lock); - if (!list_empty(&ctx->poll_list)) - io_iopoll_getevents(ctx, &nr_events, 0); - else - inflight = 0; - mutex_unlock(&ctx->uring_lock); - } else { - /* - * Normal IO, just pretend everything completed. - * We don't have to poll completions for that. - */ - nr_events = inflight; - } - - inflight -= nr_events; - if (!inflight) + mutex_lock(&ctx->uring_lock); + if (!list_empty(&ctx->poll_list)) + io_iopoll_getevents(ctx, &nr_events, 0); + if (list_empty(&ctx->poll_list)) timeout = jiffies + ctx->sq_thread_idle; + mutex_unlock(&ctx->uring_lock); } to_submit = io_sqring_entries(ctx); @@ -5152,13 +5137,31 @@ static int io_sq_thread(void *data) * more IO, we should wait for the application to * reap events and wake us up. */ - if (inflight || + if (!list_empty(&ctx->poll_list) || (!time_after(jiffies, timeout) && ret != -EBUSY && !percpu_ref_is_dying(&ctx->refs))) { cond_resched(); continue; } + /* + * While doing polled IO, before going to sleep, we need + * to check if there are new reqs added to poll_list, it + * is because reqs may have been punted to io worker and + * will be added to poll_list later, hence check the + * poll_list again, meanwhile we need to hold uring_lock + * to do this check, otherwise we may lose wakeup event + * in io_iopoll_req_issued(). + */ + if (needs_uring_lock) { + mutex_lock(&ctx->uring_lock); + if (!list_empty(&ctx->poll_list)) { + mutex_unlock(&ctx->uring_lock); + cond_resched(); + continue; + } + } + prepare_to_wait(&ctx->sqo_wait, &wait, TASK_INTERRUPTIBLE); @@ -5171,16 +5174,22 @@ static int io_sq_thread(void *data) if (!to_submit || ret == -EBUSY) { if (kthread_should_park()) { finish_wait(&ctx->sqo_wait, &wait); + if (needs_uring_lock) + mutex_unlock(&ctx->uring_lock); break; } if (signal_pending(current)) flush_signals(current); + if (needs_uring_lock) + mutex_unlock(&ctx->uring_lock); schedule(); finish_wait(&ctx->sqo_wait, &wait); ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP; continue; } + if (needs_uring_lock) + mutex_unlock(&ctx->uring_lock); finish_wait(&ctx->sqo_wait, &wait); ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP; @@ -5189,8 +5198,7 @@ static int io_sq_thread(void *data) mutex_lock(&ctx->uring_lock); ret = io_submit_sqes(ctx, to_submit, NULL, -1, &cur_mm, true); mutex_unlock(&ctx->uring_lock); - if (ret > 0) - inflight += ret; + timeout = jiffies + ctx->sq_thread_idle; } set_fs(old_fs);