Re: [Xen-devel] [PATCH 2/3] timekeeping: Fix potential lost pv notification of time change

[Ingo Molnar <mingo@xxxxxxxxxx>]

* John Stultz <john.stultz@xxxxxxxxxx> wrote:

> In 780427f0e11 (Indicate that clock was set in the pvclock
> gtod notifier), logic was added to pass a CLOCK_WAS_SET
> notification to the pvclock notifier chain.
> 
> While that patch added a action flag returned from
> accumulate_nsecs_to_secs(), it only uses the returned value
> in one location, and not in the logarithmic accumulation.
> 
> This means if a leap second triggered during the logarithmic
> accumulation (which is most likely where it would happen),
> the notification that the clock was set would not make it to
> the pv notifiers.
> 
> This patch extends the logarithmic_accumulation pass down
> that action flag so proper notification will occur.
> 
> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
> Cc: Richard Cochran <richardcochran@xxxxxxxxx>
> Cc: <xen-devel@xxxxxxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx> #3.11+
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
>  kernel/time/timekeeping.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 6bad3d9..998ec751 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1295,7 +1295,7 @@ static inline unsigned int 
> accumulate_nsecs_to_secs(struct timekeeper *tk)
>   * Returns the unconsumed cycles.
>   */
>  static cycle_t logarithmic_accumulation(struct timekeeper *tk, cycle_t 
> offset,
> -                                             u32 shift)
> +                                             u32 shift, unsigned int *action)

I have two complaints about this patch:

1)

I think the 'action' name sucks because it's too obfuscated. It's only 
ever set to TK_CLOCK_WAS_SET, so why not name it more descriptively, 
i.e. 'clock_was_set'?

2)

Secondly, the proliferation of parameters passed around I think calls 
for a helper structure which would carry the (offset, shift, 
clock_was_set) triple:

        struct acc_params {
                cycle_t         offset;
                u32             shift;
                bool            clock_was_set;
        };

And then passed down like this:

>  static cycle_t logarithmic_accumulation(struct timekeeper *tk, struct 
> acc_params *params)

Agreed?

Thanks,

        Ingo

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