From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58301) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHHKB-0000te-6Z for qemu-devel@nongnu.org; Mon, 20 Jul 2015 16:06:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHHKA-00050a-0y for qemu-devel@nongnu.org; Mon, 20 Jul 2015 16:06:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60938) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHHK9-00050E-Pb for qemu-devel@nongnu.org; Mon, 20 Jul 2015 16:06:05 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id 120F2BE29A for ; Mon, 20 Jul 2015 20:06:04 +0000 (UTC) References: <1437079157-6316-1-git-send-email-ehabkost@redhat.com> <20150716230214.3a39bd79@igors-macbook-pro.local> <20150717203355.GA11994@thinpad.lan.raisama.net> <20150720090628.38e57f68@nial.brq.redhat.com> <20150720200346.GB11994@thinpad.lan.raisama.net> From: Marcel Apfelbaum Message-ID: <55AD54A9.9050209@redhat.com> Date: Mon, 20 Jul 2015 23:06:01 +0300 MIME-Version: 1.0 In-Reply-To: <20150720200346.GB11994@thinpad.lan.raisama.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] hostmem: Fix qemu_opt_get_bool() crash in host_memory_backend_init() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost , Igor Mammedov Cc: Paolo Bonzini , qemu-devel@nongnu.org, Marcel Apfelbaum On 07/20/2015 11:03 PM, Eduardo Habkost wrote: > On Mon, Jul 20, 2015 at 09:06:28AM +0200, Igor Mammedov wrote: >> On Fri, 17 Jul 2015 17:33:55 -0300 >> Eduardo Habkost wrote: >> >>> On Thu, Jul 16, 2015 at 11:02:14PM +0200, Igor Mammedov wrote: >>>> On Thu, 16 Jul 2015 17:39:17 -0300 >>>> Eduardo Habkost wrote: >>>> >>>>> This fixes the following crash, introduced by commit >>>>> 49d2e648e8087d154d8bf8b91f27c8e05e79d5a6: >>>>> >>>>> $ gdb --args qemu-system-x86_64 -machine pc,mem-merge=off -object >>>>> memory-backend-ram,id=ram-node0,size=1024 [...] >>>>> Program received signal SIGABRT, Aborted. >>>>> (gdb) bt >>>>> #0 0x00007ffff253b8c7 in raise () at /lib64/libc.so.6 >>>>> #1 0x00007ffff253d52a in abort () at /lib64/libc.so.6 >>>>> #2 0x00007ffff253446d in __assert_fail_base () at /lib64/libc.so.6 >>>>> #3 0x00007ffff2534522 in () at /lib64/libc.so.6 >>>>> #4 0x00005555558bb80a in qemu_opt_get_bool_helper >>>>> (opts=0x55555621b650, name=name@entry=0x5555558ec922 "mem-merge", >>>>> defval=defval@entry=true, del=del@entry=false) at >>>>> qemu/util/qemu-option.c:388 #5 0x00005555558bbb5a in >>>>> qemu_opt_get_bool (opts=, >>>>> name=name@entry=0x5555558ec922 "mem-merge", defval=defval@entry=true) >>>>> at qemu/util/qemu-option.c:398 #6 0x0000555555720a24 in >>>>> host_memory_backend_init (obj=0x5555562ac970) at >>>>> qemu/backends/hostmem.c:226 >>>>> >>>>> Instead of using qemu_opt_get_bool(), that didn't work with >>>>> qemu_machine_opts for a long time, we can use the machine QOM >>>>> properties directly. >>>>> >>>>> Signed-off-by: Eduardo Habkost >>>>> --- >>>>> backends/hostmem.c | 9 +++++---- >>>>> 1 file changed, 5 insertions(+), 4 deletions(-) >>>>> >>>>> diff --git a/backends/hostmem.c b/backends/hostmem.c >>>>> index 61c1ac0..38a32ed 100644 >>>>> --- a/backends/hostmem.c >>>>> +++ b/backends/hostmem.c >>>>> @@ -10,6 +10,7 @@ >>>>> * See the COPYING file in the top-level directory. >>>>> */ >>>>> #include "sysemu/hostmem.h" >>>>> +#include "hw/boards.h" >>>>> #include "qapi/visitor.h" >>>>> #include "qapi-types.h" >>>>> #include "qapi-visit.h" >>>>> @@ -223,10 +224,10 @@ static void host_memory_backend_init(Object >>>>> *obj) { >>>>> HostMemoryBackend *backend = MEMORY_BACKEND(obj); >>>>> >>>>> - backend->merge = qemu_opt_get_bool(qemu_get_machine_opts(), >>>>> - "mem-merge", true); >>>>> - backend->dump = qemu_opt_get_bool(qemu_get_machine_opts(), >>>>> - "dump-guest-core", true); >>>>> + backend->merge = >>>>> object_property_get_bool(OBJECT(current_machine), >>>> maybe use qdev_get_machine() instead of OBJECT(current_machine) >>> >>> What are the advantages you see in the extra layers of indirection of >>> qdev_get_machine()? (I am not against your proposal, but I would like to >>> understand the point of qdev_get_machine() yet.) >> current_machine might be NULL where as qdev_get_machine() always returns >> /machine object. > > In this case, I don't want "/machine" to be created as a generic > container object by accident because it must be a MachineState object. > If /machine is not initialized yet, that code should abort instead of > trying to continue. > > But that can be solved by simply ensuring qdev_get_machine() is a > TYPE_MACHINE object (see below). > >> >>> >>> I'd prefer to use something that is guaranteed to be MachineState*, >>> qdev_get_machine() returns Object*. I am even considering using >>> current_machine->mem_merge and current_machine->dump_guest_core directly >>> instead of object_property_get_bool(). That would mean extra >>> compile-time checks, instead of runtime ones. >> Check difference 'git grep qdev_get_machine' vs 'git grep current_machine'. >> I was under impression that policy was trying no to use globals unless one has to, >> and not introduce new usage in presence of other means to get object. >> > > I will send a new version using: > > MachineState *machine = MACHINE(qdev_get_machine()); > backend->merge = machine_mem_merge(machine); > backend->dump = machine_dump_guest_core(machine); > > Then we have no global variable, type safety, and no direct access to > struct fields. +1 I am considering retiring curent_machine global variable for 2.5. Thanks, Marcel >