From patchwork Thu Nov 23 19:49:31 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13466752 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 81AFBC61D85 for ; Thu, 23 Nov 2023 19:50:49 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r6Fhv-0002Eg-R3; Thu, 23 Nov 2023 14:49:51 -0500 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 1r6Fhu-0002Dm-6g for qemu-devel@nongnu.org; Thu, 23 Nov 2023 14:49:50 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r6Fhs-0000eA-Mw for qemu-devel@nongnu.org; Thu, 23 Nov 2023 14:49:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700768987; 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=iELKm7U9eRTB2aTCq/cwFbx6/wg6Jm6PVn5zF8xT8r8=; b=VXP0zizY+LKVS2zXcTM1gFWTFYrlFbVyeZ/sx0oATw9tZRj6binS1ZVnr3fDNi9q3CF9O9 7NKf8kwhxOSBIthMd7OnCHIosfjWEN7FT3GJYzJPnuXTEdf9NW4zEmMk9sc+QGhjaZo2oq MPwoIt5WsHvJqMY1bwAyIT0FQNb5FPA= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-523-Ol2H2g9fMUWvZbYCrBvKSw-1; Thu, 23 Nov 2023 14:49:44 -0500 X-MC-Unique: Ol2H2g9fMUWvZbYCrBvKSw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 262753801BCE; Thu, 23 Nov 2023 19:49:44 +0000 (UTC) Received: from localhost (unknown [10.39.192.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7EA6E1121306; Thu, 23 Nov 2023 19:49:43 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: "Michael S. Tsirkin" , David Hildenbrand , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Peter Xu , Paolo Bonzini , Fam Zheng , Stefan Hajnoczi Subject: [PATCH 4/4] dma-helpers: don't lock AioContext in dma_blk_cb() Date: Thu, 23 Nov 2023 14:49:31 -0500 Message-ID: <20231123194931.171598-5-stefanha@redhat.com> In-Reply-To: <20231123194931.171598-1-stefanha@redhat.com> References: <20231123194931.171598-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.058, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Commit abfcd2760b3e ("dma-helpers: prevent dma_blk_cb() vs dma_aio_cancel() race") acquired the AioContext lock inside dma_blk_cb() to avoid a race with scsi_device_purge_requests() running in the main loop thread. The SCSI code no longer calls dma_aio_cancel() from the main loop thread while I/O is running in the IOThread AioContext. Therefore it is no longer necessary to take this lock to protect DMAAIOCB fields. The ->cb() function also does not require the lock because blk_aio_*() and friends do not need the AioContext lock. Both hw/ide/core.c and hw/ide/macio.c also call dma_blk_io() but don't rely on it taking the AioContext lock, so this change is safe. Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake Reviewed-by: Kevin Wolf --- system/dma-helpers.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/system/dma-helpers.c b/system/dma-helpers.c index 36211acc7e..528117f256 100644 --- a/system/dma-helpers.c +++ b/system/dma-helpers.c @@ -119,13 +119,12 @@ static void dma_blk_cb(void *opaque, int ret) trace_dma_blk_cb(dbs, ret); - aio_context_acquire(ctx); dbs->acb = NULL; dbs->offset += dbs->iov.size; if (dbs->sg_cur_index == dbs->sg->nsg || ret < 0) { dma_complete(dbs, ret); - goto out; + return; } dma_blk_unmap(dbs); @@ -168,7 +167,7 @@ static void dma_blk_cb(void *opaque, int ret) trace_dma_map_wait(dbs); dbs->bh = aio_bh_new(ctx, reschedule_dma, dbs); cpu_register_map_client(dbs->bh); - goto out; + return; } if (!QEMU_IS_ALIGNED(dbs->iov.size, dbs->align)) { @@ -179,8 +178,6 @@ static void dma_blk_cb(void *opaque, int ret) dbs->acb = dbs->io_func(dbs->offset, &dbs->iov, dma_blk_cb, dbs, dbs->io_func_opaque); assert(dbs->acb); -out: - aio_context_release(ctx); } static void dma_aio_cancel(BlockAIOCB *acb)