Re: [PATCH v1] softmmu/physmem: fix memory leak in dirty_memory_extend()

[Peter Maydell]

On Tue, 27 Aug 2024 at 09:37, David Hildenbrand <david@redhat.com> wrote:
>
> As reported by Peter, we might be leaking memory when removing the
> highest RAMBlock (in the weird ram_addr_t space), and adding a new one.
>
> We will fail to realize that we already allocated bitmaps for more
> dirty memory blocks, and effectively discard the pointers to them.
>
> Fix it by getting rid of last_ram_page() and simply storing the number
> of dirty memory blocks that have been allocated. We'll store the number
> of blocks along with the actual pointer to keep it simple.
>
> Looks like this leak was introduced as we switched from using a single
> bitmap_zero_extend() to allocating multiple bitmaps:
> bitmap_zero_extend() relies on g_renew() which should have taken care of
> this.
>
> Resolves: 
> https://lkml.kernel.org/r/CAFEAcA-k7a+VObGAfCFNygQNfCKL=AfX6A4kScq=VSSK0peqPg@mail.gmail.com
> Reported-by: Peter Maydell <peter.maydell@linaro.org>
> Fixes: 5b82b703b69a ("memory: RCU ram_list.dirty_memory[] for safe RAM 
> hotplug")
> Cc: qemu-stable@nongnu.org
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: "Philippe Mathieu-Daudé" <philmd@linaro.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

I checked, and with this fix (plus various others I've sent
out last week) we can run "make check" for the x86_64-softmmu
target under asan/lsan without getting any leak reports. So
(at least to that extent)

Tested-by: Peter Maydell <peter.maydell@linaro.org>

-- PMM