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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7BE32C3ABB2 for ; Wed, 28 May 2025 19:11:58 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uKM9d-0006zq-4U; Wed, 28 May 2025 15:09:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uKM9Y-0006xH-Vs for qemu-devel@nongnu.org; Wed, 28 May 2025 15:09:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uKM9W-0004Dd-78 for qemu-devel@nongnu.org; Wed, 28 May 2025 15:09:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1748459364; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lcKMKuZuA6GGvogpVIY1T+1EE1dq2JvS5NCdHWK07UI=; b=F7xsr8L6fbiYruyIWlkXWyHTElanmDvj1HC7Iyh8h5IHjbIIRlG1CVjUakxAYRaOr9Iphv zf+MclI2CxUBaV6myQQHc1LcUcXZKqyu6Dl8UMGnUFSCpRZg7Wv+xkW6RXB3fSSerGC9pY gpEjk4Ib2wi5GZ3f5M1Tfyx0fgx2Gf4= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-96-6MeAmVKhNeq5JgpF-kvFww-1; Wed, 28 May 2025 15:09:22 -0400 X-MC-Unique: 6MeAmVKhNeq5JgpF-kvFww-1 X-Mimecast-MFC-AGG-ID: 6MeAmVKhNeq5JgpF-kvFww_1748459360 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A10101956095; Wed, 28 May 2025 19:09:20 +0000 (UTC) Received: from localhost (unknown [10.2.16.178]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 04FC3180049D; Wed, 28 May 2025 19:09:19 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Stefan Hajnoczi , hibriansong@gmail.com, Kevin Wolf , Hanna Czenczek Subject: [RFC 01/11] aio-posix: fix polling mode with fdmon-io_uring Date: Wed, 28 May 2025 15:09:06 -0400 Message-ID: <20250528190916.35864-2-stefanha@redhat.com> In-Reply-To: <20250528190916.35864-1-stefanha@redhat.com> References: <20250528190916.35864-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) DKIMWL_WL_HIGH=-2.904, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org The io_uring(7) file descriptor monitor cannot enter polling mode because it needs to submit a POLL_ADD SQE every time a file descriptor becomes active. Submitting SQEs only happens in FDMonOps->wait() outside of polling mode. Fix this using the multi-shot mechanism introduced in Linux 5.13 and liburing 2.1. Stable and enterprise Linux distros ship 5.14+ as of March 2025, so it is safe to require this. Note that fdmon-io_uring is currently not enabled at runtime and is not essential, so QEMU can still be built without it on older hosts. In multi-shot mode, a POLL_ADD SQE remains active until canceled with POLL_REMOVE. This avoids the need to submit a new SQE every time a file descriptor becomes active. When POLL_REMOVE is processed by the host kernel, the multi-shot POLL_ADD operation completes with -ECANCELED. Adjust the code slightly to take this into account. Signed-off-by: Stefan Hajnoczi --- meson.build | 2 +- util/fdmon-io_uring.c | 34 +++++++++++++++++++++------------- 2 files changed, 22 insertions(+), 14 deletions(-) diff --git a/meson.build b/meson.build index fdad3fb528..6a362b9209 100644 --- a/meson.build +++ b/meson.build @@ -1157,7 +1157,7 @@ linux_io_uring_test = ''' linux_io_uring = not_found if not get_option('linux_io_uring').auto() or have_block - linux_io_uring = dependency('liburing', version: '>=0.3', + linux_io_uring = dependency('liburing', version: '>=2.1', required: get_option('linux_io_uring'), method: 'pkg-config') if not cc.links(linux_io_uring_test) diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c index b0d68bdc44..6cd665e565 100644 --- a/util/fdmon-io_uring.c +++ b/util/fdmon-io_uring.c @@ -124,8 +124,7 @@ static AioHandler *dequeue(AioHandlerSList *head, unsigned *flags) /* * Don't clear FDMON_IO_URING_REMOVE. It's sticky so it can serve two * purposes: telling fill_sq_ring() to submit IORING_OP_POLL_REMOVE and - * telling process_cqe() to delete the AioHandler when its - * IORING_OP_POLL_ADD completes. + * telling process_cqe() to ignore IORING_OP_POLL_ADD completions. */ *flags = qatomic_fetch_and(&node->flags, ~(FDMON_IO_URING_PENDING | FDMON_IO_URING_ADD)); @@ -166,12 +165,12 @@ static void fdmon_io_uring_update(AioContext *ctx, } } -static void add_poll_add_sqe(AioContext *ctx, AioHandler *node) +static void add_poll_multishot_sqe(AioContext *ctx, AioHandler *node) { struct io_uring_sqe *sqe = get_sqe(ctx); int events = poll_events_from_pfd(node->pfd.events); - io_uring_prep_poll_add(sqe, node->pfd.fd, events); + io_uring_prep_poll_multishot(sqe, node->pfd.fd, events); io_uring_sqe_set_data(sqe, node); } @@ -213,7 +212,7 @@ static void fill_sq_ring(AioContext *ctx) while ((node = dequeue(&submit_list, &flags))) { /* Order matters, just in case both flags were set */ if (flags & FDMON_IO_URING_ADD) { - add_poll_add_sqe(ctx, node); + add_poll_multishot_sqe(ctx, node); } if (flags & FDMON_IO_URING_REMOVE) { add_poll_remove_sqe(ctx, node); @@ -234,21 +233,30 @@ static bool process_cqe(AioContext *ctx, return false; } + flags = qatomic_read(&node->flags); + /* - * Deletion can only happen when IORING_OP_POLL_ADD completes. If we race - * with enqueue() here then we can safely clear the FDMON_IO_URING_REMOVE - * bit before IORING_OP_POLL_REMOVE is submitted. + * poll_multishot cancelled by poll_remove? Or completed early because fd + * was closed before poll_remove finished? */ - flags = qatomic_fetch_and(&node->flags, ~FDMON_IO_URING_REMOVE); - if (flags & FDMON_IO_URING_REMOVE) { + if (cqe->res == -ECANCELED || cqe->res == -EBADF) { + assert(!(cqe->flags & IORING_CQE_F_MORE)); + assert(flags & FDMON_IO_URING_REMOVE); QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted); return false; } - aio_add_ready_handler(ready_list, node, pfd_events_from_poll(cqe->res)); + /* Ignore if it becomes ready during removal */ + if (flags & FDMON_IO_URING_REMOVE) { + return false; + } - /* IORING_OP_POLL_ADD is one-shot so we must re-arm it */ - add_poll_add_sqe(ctx, node); + /* Multi-shot can stop at any time, so re-arm if necessary */ + if (!(cqe->flags & IORING_CQE_F_MORE)) { + add_poll_multishot_sqe(ctx, node); + } + + aio_add_ready_handler(ready_list, node, pfd_events_from_poll(cqe->res)); return true; } -- 2.49.0