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From: Fam Zheng <famz@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [RFC PATCH 1/9] block: Add bdrv_aio_cancel_async
Date: Fri, 22 Aug 2014 09:23:36 +0800	[thread overview]
Message-ID: <20140822012336.GB3410@T430.redhat.com> (raw)
In-Reply-To: <53F5E289.8050703@redhat.com>

On Thu, 08/21 14:14, Paolo Bonzini wrote:
> Il 21/08/2014 13:56, Fam Zheng ha scritto:
> > +        BlockDriverAIOCB *save = g_new(BlockDriverAIOCB, 1);
> > +        save->cb               = acb->cb;
> > +        save->opaque           = acb->opaque;
> > +        acb->cb                = bdrv_aio_cancel_async_cb;
> > +        acb->opaque            = acb;
> > +        acb->cancel_acb_save   = save;
> 
> No need for this extra field.  You can make a struct with {acb->cb,
> acb->opaque, acb} and pass it as the opaque.  You also do not need to
> allocate it on the heap, since everything is synchronous.
> 
> > +
> > +        /* Use the synchronous version and hope our cb is called. */
> > +        acb->aiocb_info->cancel(acb);
> 
> Unfortunately, acb has been freed at this point

Oops!

> , so you'll be accessing
> a dangling pointer.  I think you need to modify all cancel
> implementations.  For example:
> 
> - return whether they have called the callback
> 
> - only free the acb if they have called the callback
> 
> - otherwise, free the acb in bdrv_aio_cancel

What about we save cb and opaque locally, and set acb->cb to a nop. When cancel
is done we can call the original cb?

Fam

  reply	other threads:[~2014-08-22  1:23 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-21 11:56 [Qemu-devel] [RFC PATCH 0/9] scsi, block: Asynchronous request cancellation Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 1/9] block: Add bdrv_aio_cancel_async Fam Zheng
2014-08-21 12:14   ` Paolo Bonzini
2014-08-22  1:23     ` Fam Zheng [this message]
2014-08-22  8:14       ` Paolo Bonzini
2014-08-22  9:37         ` Fam Zheng
2014-08-22 10:10           ` Paolo Bonzini
2014-08-22 10:51             ` Fam Zheng
2014-08-21 13:44   ` Stefan Hajnoczi
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 2/9] tests: Add testing code for bdrv_aio_cancel_async Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 3/9] iscsi: Implement .cancel_async in acb info Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 4/9] linux-aio: Implement .cancel_async Fam Zheng
2014-08-21 16:31   ` Stefan Hajnoczi
2014-08-22  4:56     ` Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 5/9] thread-pool: " Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 6/9] blkdebug: " Fam Zheng
2014-08-21 16:52   ` Stefan Hajnoczi
2014-08-22  4:29     ` Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 7/9] dma: " Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 8/9] block: Implement stub bdrv_em_co_aiocb_info.cancel_async Fam Zheng
2014-08-21 17:01   ` Stefan Hajnoczi
2014-08-22  4:28     ` Fam Zheng
2014-08-21 11:56 ` [Qemu-devel] [RFC PATCH 9/9] scsi: Cancel request asynchronously Fam Zheng
2014-08-21 12:19   ` Paolo Bonzini
2014-08-22  4:57     ` Fam Zheng

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