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SubjectRe: [PATCH v2] rcu: small rcu_dereference doc update
On Fri, 17 Apr 2015 16:38:04 +0200
Milos Vyletel <milos@redhat.com> wrote:

> Make a note stating that repeated calls of rcu_dereference() may not
> return the same pointer if update happens while in critical section.
>
> Reported-by: Jeff Haran <jeff.haran@citrix.com>
> Signed-off-by: Milos Vyletel <milos@redhat.com>

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

> ---
> Documentation/RCU/whatisRCU.txt | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
> index 88dfce1..16622c9 100644
> --- a/Documentation/RCU/whatisRCU.txt
> +++ b/Documentation/RCU/whatisRCU.txt
> @@ -256,7 +256,9 @@ rcu_dereference()
> If you are going to be fetching multiple fields from the
> RCU-protected structure, using the local variable is of
> course preferred. Repeated rcu_dereference() calls look
> - ugly and incur unnecessary overhead on Alpha CPUs.
> + ugly, do not guarantee that the same pointer will be returned
> + if an update happened while in the critical section, and incur
> + unnecessary overhead on Alpha CPUs.
>
> Note that the value returned by rcu_dereference() is valid
> only within the enclosing RCU read-side critical section.



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