Re: [patch 8/9] Documentation: Fix invalid rcu assumptions

Arnd Bergmann
2009-12-11T21:29:12Z

On Thursday 10 December 2009 00:53:26 Thomas Gleixner wrote:
> Index: linux-2.6-tip/Documentation/credentials.txt
> ===================================================================
> --- linux-2.6-tip.orig/Documentation/credentials.txt
> +++ linux-2.6-tip/Documentation/credentials.txt
> @@ -408,9 +408,6 @@ This should be used inside the RCU read
> ...
> }
>
> -A function need not get RCU read lock to use __task_cred() if it is holding a
> -spinlock at the time as this implicitly holds the RCU read lock.
> -
> Should it be necessary to hold another task's credentials for a long period of
> time, and possibly to sleep whilst doing so, then the caller should get a
> reference on them using:

How about changing the documentation to explain why you can't just use a spinlock
or local_irq_disable instead of rcu_read_lock? You explained it well in your
[patch 0/9], but that part had not occurred to me yet and having it in the kernel
sources might prevent more people from getting it wrong in the future.

Arnd