Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG

Arnd Bergmann
2024-04-15T17:33:08Z

On Mon, Apr 15, 2024, at 19:07, Christophe Leroy wrote:
> Le 15/04/2024 à 17:35, Arnd Bergmann a écrit :
>>
>> I haven't seen a good solution here. Ideally we'd just define
>> the functions unconditionally and have IS_ENABLED() take care
>> of letting the compiler drop them silently, but that doesn't
>> build because of missing struct members.
>>
>> I won't object to either an 'extern' declaration or the
>> 'BUILD_BUG_ON()' if you and others prefer that, both are better
>> than BUG() here. I still think my suggestion would be a little
>> simpler.
>
> The advantage of the BUILD_BUG() against the extern is that the error
> gets detected at buildtime. With the extern it gets detected only at
> link-time.
>
> But agree with you, the missing struct members defeats the advantages of
> IS_ENABLED().
>
> At the end, how many instances of struct timekeeper do we have in the
> system ? With a quick look I see only two instances: tkcore.timekeeper
> and shadow_timekeeper. If I'm correct, wouldn't it just be simpler to
> have the three debug struct members defined at all time ?

Sure, this version looks fine to me, and passes a simple build
test without CONFIG_DEBUG_TIMEKEEPING.

Arnd

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 84ff2844df2a..485677a98b0b 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -124,7 +124,6 @@ struct timekeeper {
u32 ntp_err_mult;
/* Flag used to avoid updating NTP twice with same second */
u32 skip_second_overflow;
-#ifdef CONFIG_DEBUG_TIMEKEEPING
long last_warning;
/*
* These simple flag variables are managed
@@ -135,7 +134,6 @@ struct timekeeper {
*/
int underflow_seen;
int overflow_seen;
-#endif
};

#ifdef CONFIG_GENERIC_TIME_VSYSCALL
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4e18db1819f8..17f7aed807e1 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -195,7 +195,6 @@ static inline u64 tk_clock_read(const struct tk_read_base *tkr)
return clock->read(clock);
}

-#ifdef CONFIG_DEBUG_TIMEKEEPING
#define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */

static void timekeeping_check_update(struct timekeeper *tk, u64 offset)
@@ -276,15 +275,6 @@ static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr)
/* timekeeping_cycles_to_ns() handles both under and overflow */
return timekeeping_cycles_to_ns(tkr, now);
}
-#else
-static inline void timekeeping_check_update(struct timekeeper *tk, u64 offset)
-{
-}
-static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr)
-{
- BUG();
-}
-#endif

/**
* tk_setup_internals - Set up internals to use clocksource clock.
@@ -2173,7 +2163,8 @@ static bool timekeeping_advance(enum timekeeping_adv_mode mode)
goto out;

/* Do some additional sanity checking */
- timekeeping_check_update(tk, offset);
+ if (IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING))
+ timekeeping_check_update(tk, offset);

/*
* With NO_HZ we may have to accumulate many cycle_intervals