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=-16.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A6AB2C433E0 for ; Wed, 3 Feb 2021 14:58:34 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id E434964F5F for ; Wed, 3 Feb 2021 14:58:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E434964F5F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:44628 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7Jc0-0007F1-Q7 for qemu-devel@archiver.kernel.org; Wed, 03 Feb 2021 09:58:32 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:59490) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7Jb2-0006ND-3q for qemu-devel@nongnu.org; Wed, 03 Feb 2021 09:57:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43157) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7Jb0-0007Fu-Ka for qemu-devel@nongnu.org; Wed, 03 Feb 2021 09:57:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612364249; 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=fxroF4jgsU9z1g8oyhxDdelIkB75a8QTQ8rvL2/L5Cg=; b=RE6+6tOQLDYfY63gdrDT5s/ljHHZcNLQz8A2ojpnZ+1EggKhoWerpVFtT6rOk4Qb+JNWSP C8O5A/SoNGazuXvxaBjaxAHiKR3yo0PCYbM/iiHtEgxFDTMaMVF/gBtHFc9GNFN7bq77pG WS4DKt35uYCMvr/hY660mQ9Fj57GEfc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-442-Q5CMaSxUOHuXSfji019WsQ-1; Wed, 03 Feb 2021 09:57:25 -0500 X-MC-Unique: Q5CMaSxUOHuXSfji019WsQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 845D9107ACF5; Wed, 3 Feb 2021 14:57:24 +0000 (UTC) Received: from localhost (ovpn-115-141.ams2.redhat.com [10.36.115.141]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2D35F5C241; Wed, 3 Feb 2021 14:57:24 +0000 (UTC) Date: Wed, 3 Feb 2021 14:57:23 +0000 From: Stefan Hajnoczi To: Greg Kurz Subject: Re: [PATCH] virtiofsd: vu_dispatch locking should never fail Message-ID: <20210203145723.GF74271@stefanha-x1.localdomain> References: <20210129155312.595980-1-groug@kaod.org> MIME-Version: 1.0 In-Reply-To: <20210129155312.595980-1-groug@kaod.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="w3uUfsyyY1Pqa/ej" Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Vivek Goyal , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --w3uUfsyyY1Pqa/ej Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jan 29, 2021 at 04:53:12PM +0100, Greg Kurz wrote: > pthread_rwlock_rdlock() and pthread_rwlock_wrlock() can fail if a > deadlock condition is detected or the current thread already owns > the lock. They can also fail, like pthread_rwlock_unlock(), if the > mutex wasn't properly initialized. None of these are ever expected > to happen with fv_VuDev::vu_dispatch_rwlock. >=20 > Some users already check the return value and assert, some others > don't. Introduce rdlock/wrlock/unlock wrappers that just do the > former and use them everywhere. >=20 > Signed-off-by: Greg Kurz What is the purpose of this commit: 1. Code cleanup/consistency? 2. Helps debug an issue that doesn't occur in production but you hit during development? 3. Needed to diagnose a real-world issue? How do you reproduce it? I wanted to check to make sure I'm not missing an issue you found with production workloads. > @@ -645,8 +662,7 @@ static void *fv_queue_thread(void *opaque) > break; > } > /* Mutual exclusion with virtio_loop() */ > - ret =3D pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwloc= k); > - assert(ret =3D=3D 0); /* there is no possible error case */ > + vu_dispatch_wrlock(qi->virtio_dev); s/vu_dispatch_wrlock/vu_dispatch_rdlock/ ? --w3uUfsyyY1Pqa/ej Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmAaudMACgkQnKSrs4Gr c8iP1Qf/dP+fCj1Zj5o51UWH4KxWXk1ywUrW0nZvmg1CWSbs2WaXADhYwfykoRmG SL1g7yphgPHRh1CuJUKU9AC4rjXwZiiRpbmV1NsYu1xS29sOrHVkvvTXkvpql6JJ EK086oCHKAKzaFxKdojoifOON/eNRueK1iB9oySTQcz5htuzN7hoOB/9HgUQE/0Z aWkNQbsVuGg20vXOKvmxvdgOkKr/OD3kyXkDCAxUeiUkQIOstV9pVPa8LAMBkCUd Vn+hVTogWtN7A6T/D5ObA9mBvcdwBur7vxA+3thtfWe8cFh3u7mLx5zot1LHWfI6 ksN/olBJ49oO0hNPguxvzpo52LiunQ== =kS/R -----END PGP SIGNATURE----- --w3uUfsyyY1Pqa/ej--