| Message ID | 1389901950-3854-5-git-send-email-mwdalton@google.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, 2014-01-16 at 11:52 -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 out of date average, modify ewma_add() by using ACCESS_ONCE to prevent 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 <eric.dumazet@gmail.com> > Signed-off-by: Michael Dalton <mwdalton@google.com> > --- > lib/average.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 out of date average, modify ewma_add() by using ACCESS_ONCE to prevent 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 <eric.dumazet@gmail.com> > Signed-off-by: Michael Dalton <mwdalton@google.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> > --- > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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;
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 <eric.dumazet@gmail.com> Signed-off-by: Michael Dalton <mwdalton@google.com> --- lib/average.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)