On Fri, Apr 17, 2015 at 10:13:50AM -0400, Steven Rostedt wrote: > On Fri, 17 Apr 2015 07:06:38 -0700 > "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote: > > > 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.ha...@citrix.com> > > > Signed-off-by: Milos Vyletel <mi...@redhat.com> > > > > 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. > > Before you queue it, there's a few articles that are screaming to be > present... > > > > > 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. > > 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. > Thanks. Corrected. Sending v2 in a bit.
Milos > -- Steve > > > > > > > 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-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
