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Date: Wed, 02 Jul 2014 15:09:37 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] ide: fix double free
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To: =?UTF-8?B?6ZmI5qKB?= <chenliang0016@icloud.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>, ChenLiang <chenliang88@huawei.com>, "Huangweidong (C)" <weidong.huang@huawei.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "Gonglei (Arei)" <arei.gonglei@huawei.com>, "stefanha@redhat.com" <stefanha@redhat.com>

Il 02/07/2014 14:54, =E9=99=88=E6=A2=81 ha scritto:
>> > The second call should have happened within dma_aio_cancel's call to
>> > bdrv_aio_cancel.  This is the real bug.
> IMO, the second need not happened within dma_aio_cancel's call to bdrv_=
aio_cancel.
> The double free will be happened if dam_aio_cancel is called.

The callback must not be invoked after bdrv_aio_cancel.  This is the=20
fundamental invariant of bdrv_aio_cancel.  All implementations of AIOCB=20
must respect it, or bugs like this one happen.

Here, either bdrv_aio_cancel was not invoked, or the invariant was broken.

The other invariant, this time in dma-helpers.c, is that dma_bdrv_cb=20
either exits with no pending AIOCB, or it exits with a non-NULL=20
dbs->acb.  If bdrv_aio_cancel was not invoked, this invariant was broken=20
because there is a pending AIOCB but it is not in dbs->acb.

Paolo