On Thu, Nov 27, 2014 at 11:15:36AM +0000, xiaofeng.yan wrote: > From: Stephen Boyd <[email protected]> > > There is a small race between when the cycle count is read from > the hardware and when the epoch stabilizes. Consider this > scenario: > > CPU0 CPU1 > ---- ---- > cyc = read_sched_clock() > cyc_to_sched_clock() > update_sched_clock() > ... > cd.epoch_cyc = cyc; > epoch_cyc = cd.epoch_cyc; > ... > epoch_ns + cyc_to_ns((cyc - epoch_cyc) > > The cyc on cpu0 was read before the epoch changed. But we > calculate the nanoseconds based on the new epoch by subtracting > the new epoch from the old cycle count. Since epoch is most likely > larger than the old cycle count we calculate a large number that > will be converted to nanoseconds and added to epoch_ns, causing > time to jump forward too much. > > Fix this problem by reading the hardware after the epoch has > stabilized. > > Cc: Russell King <[email protected]> > Signed-off-by: Stephen Boyd <[email protected]> > Signed-off-by: John Stultz <[email protected]> > --- > kernel/time/sched_clock.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-)
What is the git commit id of this patch in Linus's tree? And what stable tree(s) do you want it applied to? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
