From patchwork Thu Apr 20 11:37:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13218617 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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 80ADBC77B72 for ; Thu, 20 Apr 2023 11:49:31 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.524178.814908 (Exim 4.92) (envelope-from ) id 1ppSmn-0001dx-7O; Thu, 20 Apr 2023 11:49:13 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 524178.814908; Thu, 20 Apr 2023 11:49:13 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ppSmn-0001do-4J; Thu, 20 Apr 2023 11:49:13 +0000 Received: by outflank-mailman (input) for mailman id 524178; Thu, 20 Apr 2023 11:49:11 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ppScs-0001nK-Ff for xen-devel@lists.xenproject.org; Thu, 20 Apr 2023 11:38:58 +0000 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id eedc5052-df6f-11ed-8611-37d641c3527e; Thu, 20 Apr 2023 13:38:56 +0200 (CEST) Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-223-ugElyGhbO4WVcymr-LwNgg-1; Thu, 20 Apr 2023 07:38:51 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 92E361C0897A; Thu, 20 Apr 2023 11:38:50 +0000 (UTC) Received: from localhost (unknown [10.39.193.254]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8A8FD51E3; Thu, 20 Apr 2023 11:38:49 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: eedc5052-df6f-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681990735; 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=svW5Iqq6ywfg5XGxDCHKSniKJYjg3etTmQ7BLHFrTFw=; b=an3g+b76QwMPE/QW5urr0RtNFLf/9WPXWqCz87YYVTEjqILJC8ytc7K0rP0KXSPk2Y3KJi XDexm/xEgHwFepMeW5/HmqXBNClgcK2VVkHWTHG7TqeTKLMCLt2ZfmlLbq628U65UKT5NT Dy2BlnY35Bxsu1dHwAaRMzxx1BKBpI4= X-MC-Unique: ugElyGhbO4WVcymr-LwNgg-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Peter Lieven , Stefan Hajnoczi , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Xie Yongji , Juan Quintela , qemu-block@nongnu.org, Eduardo Habkost , Richard Henderson , David Woodhouse , Stefan Weil , Fam Zheng , Julia Suvorova , Ronnie Sahlberg , xen-devel@lists.xenproject.org, Hanna Reitz , "Dr. David Alan Gilbert" , eesposit@redhat.com, Kevin Wolf , Marcel Apfelbaum , Stefano Stabellini , Paul Durrant , Aarushi Mehta , "Michael S. Tsirkin" , Anthony Perard , "Richard W.M. Jones" , Coiby Xu , Stefano Garzarella Subject: [PATCH v3 14/20] block/export: don't require AioContext lock around blk_exp_ref/unref() Date: Thu, 20 Apr 2023 07:37:26 -0400 Message-Id: <20230420113732.336620-15-stefanha@redhat.com> In-Reply-To: <20230420113732.336620-1-stefanha@redhat.com> References: <20230420113732.336620-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 The FUSE export calls blk_exp_ref/unref() without the AioContext lock. Instead of fixing the FUSE export, adjust blk_exp_ref/unref() so they work without the AioContext lock. This way it's less error-prone. Suggested-by: Paolo Bonzini Signed-off-by: Stefan Hajnoczi --- include/block/export.h | 2 ++ block/export/export.c | 13 ++++++------- block/export/vduse-blk.c | 4 ---- 3 files changed, 8 insertions(+), 11 deletions(-) diff --git a/include/block/export.h b/include/block/export.h index 7feb02e10d..f2fe0f8078 100644 --- a/include/block/export.h +++ b/include/block/export.h @@ -57,6 +57,8 @@ struct BlockExport { * Reference count for this block export. This includes strong references * both from the owner (qemu-nbd or the monitor) and clients connected to * the export. + * + * Use atomics to access this field. */ int refcount; diff --git a/block/export/export.c b/block/export/export.c index e3fee60611..edb05c9268 100644 --- a/block/export/export.c +++ b/block/export/export.c @@ -201,11 +201,10 @@ fail: return NULL; } -/* Callers must hold exp->ctx lock */ void blk_exp_ref(BlockExport *exp) { - assert(exp->refcount > 0); - exp->refcount++; + assert(qatomic_read(&exp->refcount) > 0); + qatomic_inc(&exp->refcount); } /* Runs in the main thread */ @@ -227,11 +226,10 @@ static void blk_exp_delete_bh(void *opaque) aio_context_release(aio_context); } -/* Callers must hold exp->ctx lock */ void blk_exp_unref(BlockExport *exp) { - assert(exp->refcount > 0); - if (--exp->refcount == 0) { + assert(qatomic_read(&exp->refcount) > 0); + if (qatomic_fetch_dec(&exp->refcount) == 1) { /* Touch the block_exports list only in the main thread */ aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh, exp); @@ -339,7 +337,8 @@ void qmp_block_export_del(const char *id, if (!has_mode) { mode = BLOCK_EXPORT_REMOVE_MODE_SAFE; } - if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE && exp->refcount > 1) { + if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE && + qatomic_read(&exp->refcount) > 1) { error_setg(errp, "export '%s' still in use", exp->id); error_append_hint(errp, "Use mode='hard' to force client " "disconnect\n"); diff --git a/block/export/vduse-blk.c b/block/export/vduse-blk.c index 35dc8fcf45..611430afda 100644 --- a/block/export/vduse-blk.c +++ b/block/export/vduse-blk.c @@ -44,9 +44,7 @@ static void vduse_blk_inflight_inc(VduseBlkExport *vblk_exp) { if (qatomic_fetch_inc(&vblk_exp->inflight) == 0) { /* Prevent export from being deleted */ - aio_context_acquire(vblk_exp->export.ctx); blk_exp_ref(&vblk_exp->export); - aio_context_release(vblk_exp->export.ctx); } } @@ -57,9 +55,7 @@ static void vduse_blk_inflight_dec(VduseBlkExport *vblk_exp) aio_wait_kick(); /* Now the export can be deleted */ - aio_context_acquire(vblk_exp->export.ctx); blk_exp_unref(&vblk_exp->export); - aio_context_release(vblk_exp->export.ctx); } }