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memory: do not add a reference to the owner of aliased regions

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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 <mst@redhat.com>
Tested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-07-27 16:29:56 +02:00
parent 55875fc4ca
commit 52c91dac6b
1 changed files with 0 additions and 7 deletions
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7
memory.c
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@ -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;
}