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Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock |
Date: |
Mon, 06 May 2013 13:11:10 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2013-05-06 12:58, Paolo Bonzini wrote:
> Il 06/05/2013 12:56, Jan Kiszka ha scritto:
>>> The problem is that even if I/O for a region is supposed to happen
>>> within the BQL, lookup can happen outside the BQL. Lookup will use the
>>> region even if it is just to discard it:
>>>
>>> VCPU thread (under BQL) device thread
>>>
>>> --------------------------------------------------------------------------------------
>>> flatview_ref
>>> memory_region_find returns
>>> d->mr
>>> memory_region_ref(d->mr) /*
>>> nop */
>>> qdev_free(d)
>>> object_unparent(d)
>>> unrealize(d)
>>> memory_region_del_subregion(d->mr)
>>> FlatView updated, d->mr not in the new view
>>>
>>> flatview_unref
>>> memory_region_unref(d->mr)
>>> object_unref(d)
>>> free(d)
>>> if (!d->mr->is_ram) {
>>> /* BAD! */
>>>
>>> memory_region_unref(d->mr) /* nop */
>>> return error
>>> }
>>>
>>>
>>> Here, the memory region is dereferenced *before* we know that it is BQL-free
>>> (in fact, exactly to ascertain whether it is BQL-free).
>>
>> Both flatview update and lookup *plus* locking type evaluation (i.e.
>> memory region dereferencing) always happen under the address space lock.
>> See Pingfan's patch.
>
> That's true of address_space_rw/map, but I don't think it holds for
> memory_region_find.
It has to, or it would be broken: Either it is called on a region that
supports reference counting and, thus, increments the counter before
returning, or it has to be called with the BQL held.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, (continued)
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/02
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, liu ping fan, 2013/05/03
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/03
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/04
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/04
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock,
Jan Kiszka <=
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Jan Kiszka, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, liu ping fan, 2013/05/05
- Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock, liu ping fan, 2013/05/05