Re: [Qemu-devel] [PATCH] Delete IOHandlers after potentially running them

[Anthony Liguori]

On 11/03/2010 09:29 AM, Stefan Hajnoczi wrote:
> Since commit 4bed9837309e58d208183f81d8344996744292cf an .fd_read()
> handler that deletes its IOHandler is exposed to .fd_write() being
> called on the deleted IOHandler.
>
> This patch fixes deletion so that .fd_read() and .fd_write() are never
> called on an IOHandler that is marked for deletion.
>
> Signed-off-by: Stefan Hajnoczi<address@hidden>
> ---
>   vl.c |   15 ++++++++-------
>   1 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/vl.c b/vl.c
> index 7038952..6f56123 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1252,17 +1252,18 @@ void main_loop_wait(int nonblocking)
>           IOHandlerRecord *pioh;
>
>           QLIST_FOREACH_SAFE(ioh,&io_handlers, next, pioh) {
> -            if (ioh->deleted) {
> -                QLIST_REMOVE(ioh, next);
> -                qemu_free(ioh);
> -                continue;
> -            }
> -            if (ioh->fd_read&&  FD_ISSET(ioh->fd,&rfds)) {
> +            if (!ioh->deleted&&  ioh->fd_read&&  FD_ISSET(ioh->fd,&rfds)) {
>                   ioh->fd_read(ioh->opaque);
>               }
> -            if (ioh->fd_write&&  FD_ISSET(ioh->fd,&wfds)) {
> +            if (!ioh->deleted&&  ioh->fd_write&&  FD_ISSET(ioh->fd,&wfds)) {
>                   ioh->fd_write(ioh->opaque);
>               }
> +
> +            /* Do this last in case read/write handlers marked it for deletion 
> */
> +            if (ioh->deleted) {
> +                QLIST_REMOVE(ioh, next);
> +                qemu_free(ioh);
> +            }
>           }
>    

This isn't enough.  If you end up with a handler deleting the next 
pointer and the current pointer, you'll end up running off the end of 
the list.

The original commit should be reverted.

Regards,

Anthony Liguori

>       }
>
>