On Wed, Aug 24, 2022 at 04:52:30PM +0800, Bin Meng wrote:
> From: Bin Meng <bin.m...@windriver.com>
>
> Fix the logic in qemu_add_wait_object() to avoid adding the same
> HANDLE twice, as the behavior is undefined when passing an array
> that contains same HANDLEs to WaitForMultipleObjects() API.
Have you encountered this problem in the real world, or is this
just a flaw you spotted through code inspection ?
Essentially I'm wondering if there's any known caller that is
making this mistake of adding it twice ?
>
> Signed-off-by: Bin Meng <bin.m...@windriver.com>
> ---
>
> Changes in v3:
> - new patch: avoid adding the same HANDLE twice
>
> include/qemu/main-loop.h | 2 ++
> util/main-loop.c | 10 ++++++++++
> 2 files changed, 12 insertions(+)
>
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index c50d1b7e3a..db8d380550 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -157,6 +157,8 @@ typedef void WaitObjectFunc(void *opaque);
> * in the main loop's calls to WaitForMultipleObjects. When the handle
> * is in a signaled state, QEMU will call @func.
> *
> + * If the same HANDLE is added twice, this function returns -1.
> + *
> * @handle: The Windows handle to be observed.
> * @func: A function to be called when @handle is in a signaled state.
> * @opaque: A pointer-size value that is passed to @func.
> diff --git a/util/main-loop.c b/util/main-loop.c
> index cb018dc33c..dae33a8daf 100644
> --- a/util/main-loop.c
> +++ b/util/main-loop.c
> @@ -373,10 +373,20 @@ static WaitObjects wait_objects = {0};
>
> int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
> {
> + int i;
> WaitObjects *w = &wait_objects;
> +
> if (w->num >= MAXIMUM_WAIT_OBJECTS) {
> return -1;
> }
> +
> + for (i = 0; i < w->num; i++) {
> + /* check if the same handle is added twice */
> + if (w->events[i] == handle) {
> + return -1;
> + }
> + }
> +
> w->events[w->num] = handle;
> w->func[w->num] = func;
> w->opaque[w->num] = opaque;
> --
> 2.34.1
>
>
With regards,
Daniel
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