On Thu, Jan 16, 2014 at 11:52:29AM -0800, Michael Dalton wrote: > To ensure ewma_read() without a lock returns a valid but possibly > out of date average, modify ewma_add() by using ACCESS_ONCE to prevent > intermediate wrong values from being written to avg->internal. > > Suggested-by: Eric Dumazet <[email protected]> > Signed-off-by: Michael Dalton <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]> > --- > lib/average.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/lib/average.c b/lib/average.c > index 99a67e6..114d1be 100644 > --- a/lib/average.c > +++ b/lib/average.c > @@ -53,8 +53,10 @@ EXPORT_SYMBOL(ewma_init); > */ > struct ewma *ewma_add(struct ewma *avg, unsigned long val) > { > - avg->internal = avg->internal ? > - (((avg->internal << avg->weight) - avg->internal) + > + unsigned long internal = ACCESS_ONCE(avg->internal); > + > + ACCESS_ONCE(avg->internal) = internal ? > + (((internal << avg->weight) - internal) + > (val << avg->factor)) >> avg->weight : > (val << avg->factor); > return avg; > -- > 1.8.5.2 _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
