Re: [PATCH 1/4] module: implement module_inhibit_unload()

Jonathan Corbet
2007-09-24T22:00:20Z

Hi, Tejun,

I was just looking over these changes...

> + /* Don't proceed till inhibition is lifted. */
> + add_wait_queue(&module_unload_wait, &wait);
> + set_current_state(TASK_UNINTERRUPTIBLE);
> + if (atomic_read(&module_unload_inhibit_cnt))
> + schedule();
> + __set_current_state(TASK_RUNNING);
> + remove_wait_queue(&module_unload_wait, &wait);
> +
> + mutex_lock(&module_mutex);

Maybe I'm missing something, but this looks racy to me. There's no
check after schedule() to see if module_unload_inhibit_cnt is really
zero, and nothing to keep somebody else from slipping in and raising it
again afterward.

Given your description of this tool as a "sledgehammer," might it not be
easier to just take and hold module_mutex for the duration of the unload
block?

jon