On Fri, Apr 17, 2015 at 12:33:36PM +0200, Milos Vyletel 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@xxxxxxxxxx> > Signed-off-by: Milos Vyletel <milos@xxxxxxxxxx> Hmmm... Seems like that should be obvious, but on the other hand, I have been using RCU for more than twenty years, so my obviousness sensors might need recalibration. Queued for 4.2. Thanx, Paul > --- > 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..82b1b2c 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 same pointer will be returned > + if update happened while in 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. > -- > 2.1.0 > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
