From patchwork Mon Mar 16 09:03:33 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fam Zheng X-Patchwork-Id: 450431 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 36DA21400B6 for ; Mon, 16 Mar 2015 20:06:47 +1100 (AEDT) Received: from localhost ([::1]:47952 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YXQyz-0007xA-Ba for incoming@patchwork.ozlabs.org; Mon, 16 Mar 2015 05:06:45 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54388) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YXQwA-0003DT-N8 for qemu-devel@nongnu.org; Mon, 16 Mar 2015 05:03:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YXQw3-0000Mv-LS for qemu-devel@nongnu.org; Mon, 16 Mar 2015 05:03:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57647) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YXQw3-0000Mr-GO for qemu-devel@nongnu.org; Mon, 16 Mar 2015 05:03:43 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 2B4F1C1F7D for ; Mon, 16 Mar 2015 09:03:43 +0000 (UTC) Received: from ad.nay.redhat.com (dhcp-14-137.nay.redhat.com [10.66.14.137]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t2G93dXc013599; Mon, 16 Mar 2015 05:03:41 -0400 From: Fam Zheng To: qemu-devel@nongnu.org Date: Mon, 16 Mar 2015 17:03:33 +0800 Message-Id: <1426496617-10702-2-git-send-email-famz@redhat.com> In-Reply-To: <1426496617-10702-1-git-send-email-famz@redhat.com> References: <1426496617-10702-1-git-send-email-famz@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: Paolo Bonzini Subject: [Qemu-devel] [PATCH v4 1/5] exec: Atomic access to bounce buffer X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org There could be a race condition when two processes call address_space_map concurrently and both want to use the bounce buffer. Add an in_use flag in BounceBuffer to sync it. Signed-off-by: Fam Zheng --- exec.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/exec.c b/exec.c index e97071a..8d21eff 100644 --- a/exec.c +++ b/exec.c @@ -2483,6 +2483,7 @@ typedef struct { void *buffer; hwaddr addr; hwaddr len; + bool in_use; } BounceBuffer; static BounceBuffer bounce; @@ -2571,7 +2572,7 @@ void *address_space_map(AddressSpace *as, l = len; mr = address_space_translate(as, addr, &xlat, &l, is_write); if (!memory_access_is_direct(mr, is_write)) { - if (bounce.buffer) { + if (atomic_xchg(&bounce.in_use, true)) { return NULL; } /* Avoid unbounded allocations */ @@ -2641,6 +2642,7 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len, qemu_vfree(bounce.buffer); bounce.buffer = NULL; memory_region_unref(bounce.mr); + atomic_mb_set(&bounce.in_use, false); cpu_notify_map_clients(); }