From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48528) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YXNdD-0006eo-N4 for qemu-devel@nongnu.org; Mon, 16 Mar 2015 01:32:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YXNd7-0003ca-JH for qemu-devel@nongnu.org; Mon, 16 Mar 2015 01:32:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50607) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YXNd7-0003cT-E4 for qemu-devel@nongnu.org; Mon, 16 Mar 2015 01:31:57 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 0851A8F312 for ; Mon, 16 Mar 2015 05:31:56 +0000 (UTC) From: Fam Zheng Date: Mon, 16 Mar 2015 13:31:47 +0800 Message-Id: <1426483910-24597-2-git-send-email-famz@redhat.com> In-Reply-To: <1426483910-24597-1-git-send-email-famz@redhat.com> References: <1426483910-24597-1-git-send-email-famz@redhat.com> Subject: [Qemu-devel] [PATCH v3 1/4] exec: Atomic access to bounce buffer List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Paolo Bonzini 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 | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/exec.c b/exec.c index e97071a..4080044 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; @@ -2571,9 +2572,10 @@ 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; } + smp_mb(); /* Avoid unbounded allocations */ l = MIN(l, TARGET_PAGE_SIZE); bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l); @@ -2641,6 +2643,7 @@ 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(); } -- 1.9.3