Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 18 Jun 2015 04:07:58 -0700 | Subject | Re: [RFC/INCOMPLETE 01/13] context_tracking: Add context_tracking_assert_state |
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On Thu, Jun 18, 2015 at 2:57 AM, Ingo Molnar <mingo@kernel.org> wrote: > > * Andy Lutomirski <luto@amacapital.net> wrote: > >> On Wed, Jun 17, 2015 at 2:41 AM, Ingo Molnar <mingo@kernel.org> wrote: >> > >> > * Andy Lutomirski <luto@kernel.org> wrote: >> > >> >> This will let us sprinkle sanity checks around the kernel without >> >> making too much of a mess. >> >> >> >> Signed-off-by: Andy Lutomirski <luto@kernel.org> >> >> --- >> >> include/linux/context_tracking.h | 8 ++++++++ >> >> 1 file changed, 8 insertions(+) >> >> >> >> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h >> >> index 2821838256b4..0fbea4b152e1 100644 >> >> --- a/include/linux/context_tracking.h >> >> +++ b/include/linux/context_tracking.h >> >> @@ -57,6 +57,13 @@ static inline void context_tracking_task_switch(struct task_struct *prev, >> >> if (context_tracking_is_enabled()) >> >> __context_tracking_task_switch(prev, next); >> >> } >> >> + >> >> +static inline void context_tracking_assert_state(enum ctx_state state) >> >> +{ >> >> + rcu_lockdep_assert(!context_tracking_is_enabled() || >> >> + this_cpu_read(context_tracking.state) == state, >> >> + "context tracking state was wrong"); >> >> +} >> > >> > Please don't introduce assert() style debug check interfaces! >> > >> > (And RCU should be fixed too I suspect.) >> > >> > They are absolutely horrible on the brain when mixed with WARN_ON() interfaces, >> > which are the dominant runtime check interface in the kernel. >> > >> > Instead make it something like: >> > >> > #define ct_state() (this_cpu_read(context_tracking.state)) >> > >> > #define CT_WARN_ON(cond) \ >> > WARN_ON(context_tracking_is_enabled() && (cond)) >> > >> > and then the debug checks can be written as: >> > >> > CT_WARN_ON(ct_state() != CONTEXT_KERNEL); >> > >> > This is IMHO _far_ more readable than: >> > >> > context_tracking_assert_state(CONTEXT_KERNEL); >> > >> > ok? >> > >> > (Assuming people will accept 'ct/CT' as an abbreviation for context tracking.) >> >> Hmm, ok I guess. The part I don't like is having ct_state() at all on >> non-context-tracking kernels -- it seems like it's asking for trouble. > > Well: > > - if # CONFIG_CONTEXT_TRACKING is not se, then CT_WARN_ON() does nothing. > > - if CONFIG_CONTEXT_TRACKING=y, but !context_tracking_is_enabled(), then > CT_WARN_ON() will evaluate 'cond', but won't calculate it. > > - only if CONFIG_CONTEXT_TRACKING=y && context_tracking_is_enabled() should we > get as far as ct_state() evaluation. > > so I'm not sure I see the problem you are seeing. > >> We could make CT_WARN_ON not even evaluate its argument if >> !CONFIG_CONTEXT_TRACKING, but then we still have ct_state() returning garbage if >> !context_tracking_is_enabled(). > > My understanding is that if !context_tracking_is_enabled() then the compiler > should not even try to evaluate the rest. This is why doing a NULL pointer check > like this is safe:
I'm fine with everything you just covered. My only objection is that, if ct_state() exists, then someone might call it outside CT_WARN_ON, in which case it will break on non-context-tracking setups.
--Andy
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