From nobody Tue Feb 10 04:13:55 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1495461542637291.9605231675332; Mon, 22 May 2017 06:59:02 -0700 (PDT) Received: from localhost ([::1]:43168 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dCnrR-0007r9-DE for importer@patchew.org; Mon, 22 May 2017 09:59:01 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59779) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dCnpy-0006qj-1i for qemu-devel@nongnu.org; Mon, 22 May 2017 09:57:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dCnpx-0005T9-58 for qemu-devel@nongnu.org; Mon, 22 May 2017 09:57:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39114) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dCnpr-0005RW-HM; Mon, 22 May 2017 09:57:23 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 49C4881252; Mon, 22 May 2017 13:57:22 +0000 (UTC) Received: from localhost (ovpn-116-229.ams2.redhat.com [10.36.116.229]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1BC23777F8; Mon, 22 May 2017 13:57:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 49C4881252 Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=stefanha@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 49C4881252 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Date: Mon, 22 May 2017 14:57:04 +0100 Message-Id: <20170522135704.842-5-stefanha@redhat.com> In-Reply-To: <20170522135704.842-1-stefanha@redhat.com> References: <20170522135704.842-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 22 May 2017 13:57:22 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v3 4/4] migration: use bdrv_drain_all_begin/end() instead bdrv_drain_all() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Paolo Bonzini , Fam Zheng , Stefan Hajnoczi , qemu-block@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" blk/bdrv_drain_all() only takes effect for a single instant and then resumes block jobs, guest devices, and other external clients like the NBD server. This can be handy when performing a synchronous drain before terminating the program, for example. Monitor commands usually need to quiesce I/O across an entire code region so blk/bdrv_drain_all() is not suitable. They must use bdrv_drain_all_begin/end() to mark the region. This prevents new I/O requests from slipping in or worse - block jobs completing and modifying the graph. I audited other blk/bdrv_drain_all() callers but did not find anything that needs a similar fix. This patch fixes the savevm/loadvm commands. Although I haven't encountered a read world issue this makes the code safer. Suggested-by: Kevin Wolf Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake --- migration/savevm.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/migration/savevm.c b/migration/savevm.c index 3ca319f..c7c5ea5 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -2113,6 +2113,8 @@ int save_vmstate(const char *name, Error **errp) } vm_stop(RUN_STATE_SAVE_VM); =20 + bdrv_drain_all_begin(); + aio_context_acquire(aio_context); =20 memset(sn, 0, sizeof(*sn)); @@ -2171,6 +2173,9 @@ int save_vmstate(const char *name, Error **errp) if (aio_context) { aio_context_release(aio_context); } + + bdrv_drain_all_end(); + if (saved_vm_running) { vm_start(); } @@ -2279,20 +2284,21 @@ int load_vmstate(const char *name, Error **errp) } =20 /* Flush all IO requests so they don't interfere with the new state. = */ - bdrv_drain_all(); + bdrv_drain_all_begin(); =20 ret =3D bdrv_all_goto_snapshot(name, &bs); if (ret < 0) { error_setg(errp, "Error %d while activating snapshot '%s' on '%s'", ret, name, bdrv_get_device_name(bs)); - return ret; + goto err_drain; } =20 /* restore the VM state */ f =3D qemu_fopen_bdrv(bs_vm_state, 0); if (!f) { error_setg(errp, "Could not open VM state file"); - return -EINVAL; + ret =3D -EINVAL; + goto err_drain; } =20 qemu_system_reset(VMRESET_SILENT); @@ -2303,6 +2309,8 @@ int load_vmstate(const char *name, Error **errp) qemu_fclose(f); aio_context_release(aio_context); =20 + bdrv_drain_all_end(); + migration_incoming_state_destroy(); if (ret < 0) { error_setg(errp, "Error %d while loading VM state", ret); @@ -2310,6 +2318,10 @@ int load_vmstate(const char *name, Error **errp) } =20 return 0; + +err_drain: + bdrv_drain_all_end(); + return ret; } =20 void vmstate_register_ram(MemoryRegion *mr, DeviceState *dev) --=20 2.9.3