Messages in this thread | | | Date | Fri, 17 Apr 2015 10:41:30 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] rcu: small rcu_dereference doc update |
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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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