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SubjectRe: [PATCH] xen: avoid deadlock in xenbus
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On 07/28/2017 10:53 AM, Juergen Gross wrote:
> When starting the xenwatch thread a theoretical deadlock situation is
> possible:
>
> xs_init() contains:
>
> task = kthread_run(xenwatch_thread, NULL, "xenwatch");
> if (IS_ERR(task))
> return PTR_ERR(task);
> xenwatch_pid = task->pid;
>
> And xenwatch_thread() does:
>
> mutex_lock(&xenwatch_mutex);
> ...
> event->handle->callback();
> ...
> mutex_unlock(&xenwatch_mutex);
>
> The callback could call unregister_xenbus_watch() which does:
>
> ...
> if (current->pid != xenwatch_pid)
> mutex_lock(&xenwatch_mutex);
> ...
>
> In case a watch is firing before xenwatch_pid could be set and the
> callback of that watch unregisters a watch, then a self-deadlock would
> occur.
>
> Avoid this by setting xenwatch_pid in xenwatch_thread().
>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

+stable?

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