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Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners rema

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 6/8] memory: Sanity check that no listeners remain on a destroyed AddressSpace
Date: Mon, 13 May 2013 13:07:20 +0100

On 13 May 2013 12:48, David Gibson <address@hidden> wrote:
> On Mon, May 13, 2013 at 12:10:10PM +0100, Peter Maydell wrote:
>> Hmm, is this the ideal semantics? Typically the owner of the
>> MemoryListener isn't the owner of the AddressSpace so it isn't
>> necessarily in a position to guarantee that it can unregister
>> the listener before the address space is destroyed. In fact
>> as the listener API is currently documented, the filter
>> argument is just an optimisation to save the callbacks having
>> to filter out irrelevant information themselves.
> If so, then it's broken by design.  There's no guarantee that after an
> AddressSpace is destroyed another one won't be created at the same
> address (in fact, depending on your malloc() implementation, it could
> be very likely).  So references by pointer to an object *must* be
> removed before the object itself is freed.

Mmm. Looking through the code it turns out we don't actually
make use of the ability to pass NULL as a filter (except in
target-arm/kvm.c which was just me being lazy and not passing
in the system address space). Perhaps we should just drop that
capability, at which point you have a clearer "you are listening
on one AS and you must make sure you arrange to unregister before
that AS goes away" API definition?

-- PMM

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