Re: [PATCH net-next 3/5] be2net: fix erx->rx_drops_no_frags wrap around
From: Eric Dumazet <hidden>
Date: 2011-08-22 11:43:32
Le lundi 22 août 2011 à 16:43 +0530, Sathya Perla a écrit :
quoted hunk ↗ jump to hunk
The rx_drops_no_frags HW counter for RSS rings is 16bits in HW and can wraparound often. Maintain a 32-bit accumulator in the driver to prevent frequent wraparound. Signed-off-by: Sathya Perla <redacted> --- drivers/net/ethernet/emulex/benet/be_main.c | 21 ++++++++++++++++++--- 1 files changed, 18 insertions(+), 3 deletions(-)diff --git a/drivers/net/ethernet/emulex/benet/be_main.c b/drivers/net/ethernet/emulex/benet/be_main.c index 2375c0c..4e588d8 100644 --- a/drivers/net/ethernet/emulex/benet/be_main.c +++ b/f@@ -378,6 +378,17 @@ static void populate_lancer_stats(struct be_adapter *adapter) pport_stats->rx_drops_too_many_frags_lo; } +static void accumulate_16bit_val(u32 *acc, u16 val) +{ +#define lo(x) (x & 0xFFFF) +#define hi(x) (x & 0xFFFF0000) + bool wrapped = val < lo(*acc); + + *acc = hi(*acc) + val; + if (wrapped) + *acc += 65536; +} +
This adds a race for lockless SNMP readers (in be_get_stats64()) They can see the 32bit value going backward. You have to be very careful to read the *acc once, and write it once.