bonding: refine bond_fold_stats() wrap detection

Some device drivers reset their stats at down/up events, possibly
fooling bonding stats, since they operate with relative deltas.

It is nearly not possible to fix drivers, since some of them compute the
tx/rx counters based on per rx/tx queue stats, and the queues can be
reconfigured (ethtool -L) between the down/up sequence.

Lets avoid accumulating 'negative' values that render bonding stats
useless.

It is better to lose small deltas, assuming the bonding stats are
fetched at a reasonable frequency.

Fixes: 5f0c5f73e5ef ("bonding: make global bonding stats more reliable")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 6cea964..27359da 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3332,12 +3332,17 @@ static void bond_fold_stats(struct rtnl_link_stats64 *_res,
        for (i = 0; i < sizeof(*_res) / sizeof(u64); i++) {
                u64 nv = new[i];
                u64 ov = old[i];
+               s64 delta = nv - ov;
 
                /* detects if this particular field is 32bit only */
                if (((nv | ov) >> 32) == 0)
-                       res[i] += (u32)nv - (u32)ov;
-               else
-                       res[i] += nv - ov;
+                       delta = (s64)(s32)((u32)nv - (u32)ov);
+
+               /* filter anomalies, some drivers reset their stats
+                * at down/up events.
+                */
+               if (delta > 0)
+                       res[i] += delta;
        }
 }