linux-kernel - Re: v4.4.12-rt20 build: 0 failures 5 warnings (v4.4.12-rt20)

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Date:	Fri, 15 Jul 2016 14:05:27 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linaro-kernel@...ts.linaro.org,
	Build bot for Mark Brown <broonie@...nel.org>,
	kernel-build-reports@...ts.linaro.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: v4.4.12-rt20 build: 0 failures 5 warnings (v4.4.12-rt20)

* Arnd Bergmann | 2016-07-15 09:07:20 [+0200]:

>Cc linux-rt-users@...r.kernel.org, let's have a look at the individual warnings:
thanks.

>
>> Warnings Summary: 5
>> 	  9 ../kernel/sched/core.c:3473:12: warning: 'preemptible_lazy' defined but not used [-Wunused-function]
>
>This was introduced by the rt patchset, I'd suggest adding a fix to the next
>v4.4-rt release. This is almost certainly harmless.

has been adressed in 4.6.4-rt8 and is harmless.

>> 	  2 ../include/linux/spinlock.h:246:3: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
>
>I'm missing context here, so I don't know what caused it, but the warning is
>not present in v4.4.12 (without -rt), so it's worth looking into.

the full log:

|In file included from include/linux/seqlock.h:35:0,
|                 from include/linux/time.h:5,
|                 from include/uapi/linux/timex.h:56,
|                 from include/linux/timex.h:56,
|                 from include/linux/sched.h:19,
|                 from arch/arm64/include/asm/compat.h:25,
|                 from arch/arm64/include/asm/stat.h:23,
|                 from include/linux/stat.h:5,
|                 from include/linux/module.h:10,
|                 from drivers/tty/serial/amba-pl011.c:37:
|drivers/tty/serial/amba-pl011.c: In function ‘pl011_console_write’:
|include/linux/spinlock.h:246:3: warning: ‘flags’ may be used uninitialized in this function [-Wmaybe-uninitialized]
|   _raw_spin_unlock_irqrestore(lock, flags); \
|   ^
|drivers/tty/serial/amba-pl011.c:2065:16: note: ‘flags’ was declared here
|  unsigned long flags;
|                ^

and relevant part of the source:
|pl011_console_write(struct console *co, const char *s, unsigned int count)
|{
…
|        unsigned long flags;
|        int locked = 1;
|
…
|        if (uap->port.sysrq)
|                locked = 0;
|        else if (oops_in_progress)
|                locked = spin_trylock_irqsave(&uap->port.lock, flags);
|        else
|                spin_lock_irqsave(&uap->port.lock, flags);
…
|        if (locked)
|                spin_unlock_irqrestore(&uap->port.lock, flags);
…
|}

looks like a false positive to me.

>	Arnd

Sebastian