If two consecutive reads of the counter are the same, it is also not an overflow. "systimel_1 < systimel_2" should be "systimel_1 <= systimel_2".
Before the patch, we could perform an *erroneous* correction: Let's say that systimel_1 == systimel_2 == 0xffffffff. "systimel_1 < systimel_2" is false, we think it's an overflow, we read "systimeh = er32(SYSTIMH)" which meanwhile had incremented, and use "(systimeh << 32) + systimel_2" value which is 2^32 too large. Signed-off-by: Denys Vlasenko <[email protected]> CC: Jeff Kirsher <[email protected]> CC: Jesse Brandeburg <[email protected]> CC: Shannon Nelson <[email protected]> CC: Carolyn Wyborny <[email protected]> CC: Don Skidmore <[email protected]> CC: Bruce Allan <[email protected]> CC: John Ronciak <[email protected]> CC: Mitch Williams <[email protected]> CC: David S. Miller <[email protected]> CC: LKML <[email protected]> CC: [email protected] --- drivers/net/ethernet/intel/e1000e/netdev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c index 967311b..99d0e6e 100644 --- a/drivers/net/ethernet/intel/e1000e/netdev.c +++ b/drivers/net/ethernet/intel/e1000e/netdev.c @@ -4287,7 +4287,7 @@ static cycle_t e1000e_cyclecounter_read(const struct cyclecounter *cc) systimeh = er32(SYSTIMH); systimel_2 = er32(SYSTIML); /* Check for overflow. If there was no overflow, use the values */ - if (systimel_1 < systimel_2) { + if (systimel_1 <= systimel_2) { systim = (cycle_t)systimel_1; systim |= (cycle_t)systimeh << 32; } else { -- 1.8.1.4
