On Thu, 4 Jul 2013, Alex Shi wrote:
> After clocksource_find_best() introduced, it is impossible to get into
> some code path. so clean them up.
That's wrong.
> Signed-off-by: Alex Shi <alex....@intel.com>
> ---
> kernel/time/clocksource.c | 16 +---------------
> 1 file changed, 1 insertion(+), 15 deletions(-)
>
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index e713ef7..021c159 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -582,26 +582,12 @@ static void __clocksource_select(bool skipcur)
> if (!best)
> return;
>
> - /* Check for the override clocksource. */
> list_for_each_entry(cs, &clocksource_list, list) {
> if (skipcur && cs == curr_clocksource)
> continue;
> if (strcmp(cs->name, override_name) != 0)
> continue;
We need this check and it is completely unrelated to the problem
you're trying to solve.
Assume the following:
System boots with clocksource A and switches into highres mode.
Now clocksource B gets registered and B is not highres capable.
clocksource_find_best() selects again A, but we have
clocksource=B on the kernel command line to override the kernel
decision.
By removing the check, you install he non highres capable clocksource
B and kill the machine.
> - /*
> - * Check to make sure we don't switch to a non-highres
> - * capable clocksource if the tick code is in oneshot
> - * mode (highres or nohz)
> - */
> - if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
> - /* Override clocksource cannot be used. */
> - printk(KERN_WARNING "Override clocksource %s is not "
> - "HRT compatible. Cannot switch while in "
> - "HRT/NOHZ mode\n", cs->name);
> - override_name[0] = 0;
> - } else
> - /* Override clocksource can be used. */
> - best = cs;
> + best = cs;
> break;
> }
Thanks,
tglx
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