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 D960DC5AD49 for ; Mon, 2 Jun 2025 22:27:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uMDcM-0004kq-Tu; Mon, 02 Jun 2025 18:26:55 -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 1uMDcL-0004j6-5a for qemu-devel@nongnu.org; Mon, 02 Jun 2025 18:26:53 -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 1uMDcH-0003v8-JC for qemu-devel@nongnu.org; Mon, 02 Jun 2025 18:26:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1748903201; 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: in-reply-to:in-reply-to:references:references; bh=vREyzAPNyetaPudYg41WmZi10BINRamqQCyggk2mX0k=; b=H+GV12tpBPrd7IejVPMXv99OizFUJbgHNylzVWEqk+lt5n3MGg6sO/RMEmvk4SKQOvYcXy Yu6k/8XqciEdNRq6sbA6Fqq/Ae2oe68tuKmwi7F+1QigO8424C6h0L7xOsIlioE0a2cinf BlnRIRIppxiw5kDwHrVEDM7JtCikMpA= 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-636-8Cq7GLTlO3mgM6c7wCTzIQ-1; Mon, 02 Jun 2025 18:26:40 -0400 X-MC-Unique: 8Cq7GLTlO3mgM6c7wCTzIQ-1 X-Mimecast-MFC-AGG-ID: 8Cq7GLTlO3mgM6c7wCTzIQ_1748903199 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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 EE7E51956086; Mon, 2 Jun 2025 22:26:38 +0000 (UTC) Received: from localhost (unknown [10.2.16.84]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E28B419560A3; Mon, 2 Jun 2025 22:26:37 +0000 (UTC) Date: Mon, 2 Jun 2025 16:20:51 -0400 From: Stefan Hajnoczi To: Brian Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Kevin Wolf , Hanna Czenczek Subject: Re: [RFC 08/11] aio-posix: gracefully handle io_uring_queue_init() failure Message-ID: <20250602202051.GE300284@fedora> References: <20250528190916.35864-1-stefanha@redhat.com> <20250528190916.35864-9-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="Y4A/9oCcGVBQ8113" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.015, 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=ham 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 --Y4A/9oCcGVBQ8113 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jun 02, 2025 at 08:26:39AM -0400, Brian wrote: > On 5/28/25 3:09 PM, Stefan Hajnoczi wrote: > > io_uring may not be available at runtime due to system policies (e.g. > > the io_uring_disabled sysctl) or creation could fail due to file > > descriptor resource limits. > >=20 > > Handle failure scenarios as follows: > >=20 > > If another AioContext already has io_uring, then fail AioContext > > creation so that the aio_add_sqe() API is available uniformly from all > > QEMU threads. Otherwise fall back to epoll(7) if io_uring is > > unavailable. > >=20 > > Notes: > > - Update the comment about selecting the fastest fdmon implementation. > > At this point it's not about speed anymore, it's about aio_add_sqe() > > API availability. > > - Uppercase the error message when converting from error_report() to > > error_setg_errno() for consistency (but there are instances of > > lowercase in the codebase). > > - It's easier to move the #ifdefs from aio-posix.h to aio-posix.c. > >=20 > > Signed-off-by: Stefan Hajnoczi > > --- > > util/aio-posix.h | 12 ++---------- > > util/aio-posix.c | 29 ++++++++++++++++++++++++++--- > > util/fdmon-io_uring.c | 8 ++++---- > > 3 files changed, 32 insertions(+), 17 deletions(-) > >=20 > > diff --git a/util/aio-posix.h b/util/aio-posix.h > > index f9994ed79e..6f9d97d866 100644 > > --- a/util/aio-posix.h > > +++ b/util/aio-posix.h > > @@ -18,6 +18,7 @@ > > #define AIO_POSIX_H > > #include "block/aio.h" > > +#include "qapi/error.h" struct AioHandler { GPollFD pfd; @@ -72,17 > > +73,8 @@ static inline void fdmon_epoll_disable(AioContext *ctx) #endif > > /* !CONFIG_EPOLL_CREATE1 */ #ifdef CONFIG_LINUX_IO_URING -bool > > fdmon_io_uring_setup(AioContext *ctx); +void > > fdmon_io_uring_setup(AioContext *ctx, Error **errp); void > > fdmon_io_uring_destroy(AioContext *ctx); -#else -static inline bool > > fdmon_io_uring_setup(AioContext *ctx) -{ - return false; -} - -static > > inline void fdmon_io_uring_destroy(AioContext *ctx) -{ -} #endif /* > > !CONFIG_LINUX_IO_URING */ #endif /* AIO_POSIX_H */ diff --git > > a/util/aio-posix.c b/util/aio-posix.c index fa047fc7ad..44b3df61f9 > > 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -16,6 +16,7 @@ > > #include "qemu/osdep.h" > > #include "block/block.h" > > #include "block/thread-pool.h" > > +#include "qapi/error.h" > > #include "qemu/main-loop.h" > > #include "qemu/lockcnt.h" > > #include "qemu/rcu.h" > > @@ -717,17 +718,39 @@ void aio_context_setup(AioContext *ctx, Error **e= rrp) > > ctx->epollfd =3D -1; > > ctx->epollfd_tag =3D NULL; > > - /* Use the fastest fd monitoring implementation if available */ > > - if (fdmon_io_uring_setup(ctx)) { > > - return; > > +#ifdef CONFIG_LINUX_IO_URING > > + { > > + static bool need_io_uring; > > + Error *local_err =3D NULL; /* ERRP_GUARD() doesn't handle erro= r_abort */ > > + > > + /* io_uring takes precedence because it provides aio_add_sqe()= support */ > > + fdmon_io_uring_setup(ctx, &local_err); > > + if (!local_err) { > > + /* > > + * If one AioContext gets io_uring, then all AioContexts n= eed io_uring > > + * so that aio_add_sqe() support is available across all t= hreads. > > + */ > > + need_io_uring =3D true; > > + return; > > + } > > + if (need_io_uring) { > > + error_propagate(errp, local_err); > > + return; > > + } > > + > > + warn_report_err_once(local_err); /* frees local_err */ > > + local_err =3D NULL; > > } > > +#endif /* CONFIG_LINUX_IO_URING */ > Is there a problem with the logic of this code snippet? >=20 > If we fail at fdmon_io_uring_setup, specifically at io_uring_queue_init, > local_err (or errp) will be set to a non-NULL error value. In that case, > need_io_uring will be set to true, but the function will return immediate= ly. If local_err is non-NULL then this conditional is not taken: if (!local_err) { /* * If one AioContext gets io_uring, then all AioContexts need io_uring * so that aio_add_sqe() support is available across all threads. */ need_io_uring =3D true; return; } If the logic you described is correct, please rephrase it. I don't see how what you've written can happen. > As a result, the later if (need_io_uring) block will never be executed >=20 > > fdmon_epoll_setup(ctx); > > } > > void aio_context_destroy(AioContext *ctx) > > { > > +#ifdef CONFIG_LINUX_IO_URING > > fdmon_io_uring_destroy(ctx); > > +#endif > > qemu_lockcnt_lock(&ctx->list_lock); > > fdmon_epoll_disable(ctx); > > diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c > > index 2092d08d24..ef1a866a03 100644 > > --- a/util/fdmon-io_uring.c > > +++ b/util/fdmon-io_uring.c > > @@ -45,6 +45,7 @@ > > #include "qemu/osdep.h" > > #include > > +#include "qapi/error.h" > > #include "qemu/rcu_queue.h" > > #include "aio-posix.h" > > @@ -361,7 +362,7 @@ static const FDMonOps fdmon_io_uring_ops =3D { > > .gsource_dispatch =3D fdmon_io_uring_gsource_dispatch, > > }; > > -bool fdmon_io_uring_setup(AioContext *ctx) > > +void fdmon_io_uring_setup(AioContext *ctx, Error **errp) > > { > > int ret; > > @@ -369,15 +370,14 @@ bool fdmon_io_uring_setup(AioContext *ctx) > > ret =3D io_uring_queue_init(FDMON_IO_URING_ENTRIES, &ctx->fdmon_i= o_uring, 0); > > if (ret !=3D 0) { > > - return false; > > + error_setg_errno(errp, -ret, "Failed to initialize io_uring"); > > + return; > > } > > QSLIST_INIT(&ctx->submit_list); > > ctx->fdmon_ops =3D &fdmon_io_uring_ops; > > ctx->io_uring_fd_tag =3D g_source_add_unix_fd(&ctx->source, > > ctx->fdmon_io_uring.ring_fd, G_IO_IN); > > - > > - return true; > > } > > void fdmon_io_uring_destroy(AioContext *ctx) --Y4A/9oCcGVBQ8113 Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmg+B6MACgkQnKSrs4Gr c8h0pAgAlntcJSBwPZyJogZ6Euaklc/eMRRjGNr7clN5bHH0FY48kuAzuFkyCfcU NYAMhuxxySE68x7U4UjroeEaEZevL6xgsevOt/5qtgr81l52SDn+LeN1LihuOFFT kvwj15eYe2JHYb7m6nb9xxSnI2gaD6OJFuztUZlEh2swrG6Z4Ad/EAlyjEm3o3T+ jRgcQs2EITaI9JxFE+bEewhsmKEi06iZ69bvLulnMzX31u6VOO889R5D8GynycKH azvJ46pELGgGZ7rCU9RMMaRRS125o7HzawLDc4kku7CmZ0ERyGJB6lvI7R/NFvSp sWev/F7revMM41OEDyp/KGu9/EGbAA== =VTQ3 -----END PGP SIGNATURE----- --Y4A/9oCcGVBQ8113--