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Re: [Qemu-devel] [PATCH] memory: do not add a reference to the owner of
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] memory: do not add a reference to the owner of aliased regions |
Date: |
Mon, 27 Jul 2015 18:11:20 +0300 |
On Mon, Jul 27, 2015 at 04:31:15PM +0200, Paolo Bonzini wrote:
> Very often the owner of the aliased region is the same as the owner of the
> alias
> region itself. When this happens, the reference count can never go back to 0
> and
> the owner is leaked. This is for example breaking hot-unplug of virtio-pci
> devices (the device cannot be plugged back again with the same id).
>
> Another common use for alias is to transform the system I/O address space
> into an MMIO regions; in this case the aliased region never dies, so there
> is no problem. Otherwise the owner is always the same for aliasing
> and aliased region.
>
> I checked all calls to memory_region_init_alias introduced after commit
> dfde4e6 (memory: add ref/unref calls, 2013-05-06) and they do not need the
> reference in order to keep the owner of the aliased region alive.
>
> Reported-by: Michael S. Tsirkin <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
Tested-by: Michael S. Tsirkin <address@hidden>
> ---
> memory.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index 5e5f325..4eb138a 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -859,11 +859,6 @@ static void memory_region_destructor_ram(MemoryRegion
> *mr)
> qemu_ram_free(mr->ram_addr);
> }
>
> -static void memory_region_destructor_alias(MemoryRegion *mr)
> -{
> - memory_region_unref(mr->alias);
> -}
> -
> static void memory_region_destructor_ram_from_ptr(MemoryRegion *mr)
> {
> qemu_ram_free_from_ptr(mr->ram_addr);
> @@ -1272,8 +1267,6 @@ void memory_region_init_alias(MemoryRegion *mr,
> uint64_t size)
> {
> memory_region_init(mr, owner, name, size);
> - memory_region_ref(orig);
> - mr->destructor = memory_region_destructor_alias;
> mr->alias = orig;
> mr->alias_offset = offset;
> }
> --
> 2.4.3