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Message-Id: <dd6653b2-3a88-4b95-af13-c6fda5b27b39@app.fastmail.com>
Date: Thu, 11 Apr 2024 13:26:52 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Adrian Hunter" <adrian.hunter@...el.com>,
"Christophe Leroy" <christophe.leroy@...roup.eu>
Cc: "Peter Zijlstra" <peterz@...radead.org>,
"Dave Hansen" <dave.hansen@...ux.intel.com>,
"John Stultz" <jstultz@...gle.com>, "H. Peter Anvin" <hpa@...or.com>,
"Alexander Gordeev" <agordeev@...ux.ibm.com>,
"Vincenzo Frascino" <vincenzo.frascino@....com>,
"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
"Naresh Kamboju" <naresh.kamboju@...aro.org>,
"x86@...nel.org" <x86@...nel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
"Ingo Molnar" <mingo@...hat.com>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
"Christian Borntraeger" <borntraeger@...ux.ibm.com>,
"Vasily Gorbik" <gor@...ux.ibm.com>,
"Heiko Carstens" <hca@...ux.ibm.com>,
"Nicholas Piggin" <npiggin@...il.com>, "Borislav Petkov" <bp@...en8.de>,
"Andy Lutomirski" <luto@...nel.org>,
"Bjorn Helgaas" <bhelgaas@...gle.com>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Anna-Maria Gleixner" <anna-maria@...utronix.de>,
"Stephen Boyd" <sboyd@...nel.org>,
"Randy Dunlap" <rdunlap@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Sven Schnelle" <svens@...ux.ibm.com>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG
On Thu, Apr 11, 2024, at 11:27, Adrian Hunter wrote:
> On 11/04/24 11:22, Christophe Leroy wrote:
>> Le 11/04/2024 à 10:12, Christophe Leroy a écrit :
>>>
>>> Looking at the report, I think the correct fix should be to use
>>> BUILD_BUG() instead of BUG()
>>
>> I confirm the error goes away with the following change to next-20240411
>> on powerpc tinyconfig with gcc 13.2
>>
>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>> index 4e18db1819f8..3d5ac0cdd721 100644
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -282,7 +282,7 @@ 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();
>> + BUILD_BUG();
>> }
>> #endif
>>
>
> That is fragile because it depends on defined(__OPTIMIZE__),
> so it should still be:
If there is a function that is defined but that must never be
called, I think we are doing something wrong. Before
e8e9d21a5df6 ("timekeeping: Refactor timekeeping helpers"),
the #ifdef made some sense, but now the #else is not really
that useful.
Ideally we would make timekeeping_debug_get_delta() and
timekeeping_check_update() just return in case of
!IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING), but unfortunately
the code uses some struct members that are undefined then.
The patch below moves the #ifdef check into these functions,
which is not great, but it avoids defining useless
functions. Maybe there is a better way here. How about
just removing the BUG()?
Arnd
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4e18db1819f8..16c6dba64dd6 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -195,12 +195,11 @@ 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)
{
-
+#ifdef CONFIG_DEBUG_TIMEKEEPING
u64 max_cycles = tk->tkr_mono.clock->max_cycles;
const char *name = tk->tkr_mono.clock->name;
@@ -235,12 +234,19 @@ static void timekeeping_check_update(struct timekeeper *tk, u64 offset)
}
tk->overflow_seen = 0;
}
+#endif
}
static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles);
-static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr)
+static u64 __timekeeping_get_ns(const struct tk_read_base *tkr)
+{
+ return timekeeping_cycles_to_ns(tkr, tk_clock_read(tkr));
+}
+
+static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr)
{
+#ifdef CONFIG_DEBUG_TIMEKEEPING
struct timekeeper *tk = &tk_core.timekeeper;
u64 now, last, mask, max, delta;
unsigned int seq;
@@ -275,16 +281,10 @@ 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();
-}
+ return __timekeeping_get_ns(tkr);
#endif
+}
/**
* tk_setup_internals - Set up internals to use clocksource clock.
@@ -390,19 +390,6 @@ static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 c
return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift;
}
-static __always_inline u64 __timekeeping_get_ns(const struct tk_read_base *tkr)
-{
- return timekeeping_cycles_to_ns(tkr, tk_clock_read(tkr));
-}
-
-static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr)
-{
- if (IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING))
- return timekeeping_debug_get_ns(tkr);
-
- return __timekeeping_get_ns(tkr);
-}
-
/**
* update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
* @tkr: Timekeeping readout base from which we take the update
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