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Re: [PATCH v2] xen/console: Skip switching serial input to non existing domains
- To: Michal Orzel <michal.orzel@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 Mar 2023 12:11:19 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 16 Mar 2023 11:11:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.03.2023 11:26, Michal Orzel wrote:
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -490,7 +490,24 @@ static void switch_serial_input(void)
> }
> else
> {
> - console_rx++;
> + unsigned int next_rx = console_rx + 1;
> +
> + /* Skip switching serial input to non existing domains */
> + while ( next_rx < max_init_domid + 1 )
> + {
> + struct domain *d = rcu_lock_domain_by_id(next_rx - 1);
> +
> + if ( d )
> + {
> + rcu_unlock_domain(d);
> + break;
> + }
> +
> + next_rx++;
> + }
> +
> + console_rx = next_rx;
> +
> printk("*** Serial input to DOM%d", console_rx - 1);
> }
While at the first glance (when you sent it in reply to v1) it looked okay,
I'm afraid it really isn't: Please consider what happens when the last of
the DomU-s doesn't exist anymore. (You don't really check whether it still
exists, because the range check comes ahead of the existence one.) In that
case you want to move from second-to-last to Xen. I expect the entire
if/else construct wants to be inside the loop.
Jan
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