From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43885) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ej8ii-0005Eo-AP for qemu-devel@nongnu.org; Tue, 06 Feb 2018 14:16:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ej8if-0007xb-Ks for qemu-devel@nongnu.org; Tue, 06 Feb 2018 14:15:56 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:60746 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ej8if-0007x0-F6 for qemu-devel@nongnu.org; Tue, 06 Feb 2018 14:15:53 -0500 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w16JEJcV056297 for ; Tue, 6 Feb 2018 14:15:53 -0500 Received: from e15.ny.us.ibm.com (e15.ny.us.ibm.com [129.33.205.205]) by mx0b-001b2d01.pphosted.com with ESMTP id 2fygjbwcmx-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 06 Feb 2018 14:15:52 -0500 Received: from localhost by e15.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 6 Feb 2018 14:15:52 -0500 From: Michael Roth Date: Tue, 6 Feb 2018 13:14:47 -0600 In-Reply-To: <20180206191515.25830-1-mdroth@linux.vnet.ibm.com> References: <20180206191515.25830-1-mdroth@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Message-Id: <20180206191515.25830-27-mdroth@linux.vnet.ibm.com> Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PATCH 26/54] linux-user: Fix locking order in fork_start() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, christian.ehrhardt@canonical.com, Peter Maydell , Laurent Vivier From: Peter Maydell Our locking order is that the tb lock should be taken inside the mmap_lock, but fork_start() grabs locks the other way around. This means that if a heavily multithreaded guest process (such as Java) calls fork() it can deadlock, with the thread that called fork() stuck in fork_start() with the tb lock and waiting for the mmap lock, but some other thread in tb_find() with the mmap lock and waiting for the tb lock. The cpu_list_lock() should also always be taken last, not first. Fix this by making fork_start() grab the locks in the right order. The order in which we drop locks doesn't matter, so we leave fork_end() the way it is. Signed-off-by: Peter Maydell Cc: qemu-stable@nongnu.org Reviewed-by: Paolo Bonzini Reviewed-by: Alex Benn=C3=A9e Message-Id: <1512397331-15238-1-git-send-email-peter.maydell@linaro.org> Signed-off-by: Laurent Vivier (cherry picked from commit 024949caf32805f4cc3e7d363a80084b47aac1f6) Signed-off-by: Michael Roth --- linux-user/main.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/linux-user/main.c b/linux-user/main.c index 6286661bd3..146ee3e4ba 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -128,9 +128,9 @@ int cpu_get_pic_interrupt(CPUX86State *env) /* Make sure everything is in a consistent state for calling fork(). */ void fork_start(void) { - cpu_list_lock(); - qemu_mutex_lock(&tb_ctx.tb_lock); mmap_fork_start(); + qemu_mutex_lock(&tb_ctx.tb_lock); + cpu_list_lock(); } =20 void fork_end(int child) --=20 2.11.0