Re: [2.4, 2.5, USB] locking issue

[Greg KH]

On Mon, Nov 18, 2002 at 05:34:20PM +0300, Samium Gromoff wrote:
>         The possible problem is encountered in ehci-q.c and ehci-sched.c
>   in 2.4.19-pre9 and in one occurence in ehci-q.c of 2.5.47.
> 
>         the offending pattern is the same in both files:
> 
>         if (!list_empty (qtd_list)) {
>  -----------------------8<----------------------------------------------
>                 list_splice (qtd_list, &qh->qtd_list);
>                 qh_update (qh, list_entry (qtd_list->next, struct ehci_qtd, qtd\_list));
>  -----------------------8<----------------------------------------------
>         } else {
>                 qh->hw_qtd_next = qh->hw_alt_next = EHCI_LIST_END;
>         }
> 
> 
>         since list_splice() the qtd_list is diposed of its belongings and
>         immediately in the next line we rely on qtd_list->next to point
>         at an existing list_head.
> 
>         i haven`t noticed any locking out there, and i`m afraid of what
>         could result from a preemption happening between these two lines.

Um, David, any thoughts about this?

thanks,

greg k-h