On Friday, July 15, 2016 2:05:27 PM CEST Sebastian Andrzej Siewior wrote:
> * Arnd Bergmann | 2016-07-15 09:07:20 [+0200]:
>
> >Cc linux-rt-users@xxxxxxxxxxxxxxx, 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.
Ok.
> |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.
Agreed, but it's hard for the compiler to figure that out. On mainline,
we have this instead:
local_irq_save(flags);
if (uap->port.sysrq)
locked = 0;
else if (oops_in_progress)
locked = spin_trylock(&uap->port.lock);
else
spin_lock(&uap->port.lock);
…
if (locked)
spin_unlock(&uap->port.lock);
local_irq_restore(flags);
which looks like it's intentionally written to avoid the warning
and was changed by Thomas in "tty/serial/pl011: Make the locking work on RT":
http://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit/drivers/tty/serial/amba-pl011.c?h=v4.4-rt-rebase&id=7b537b66fcb12c40eb1b10eb352d570a9d34a657
Maybe there is another way to write this upstream that avoids the
warning.
Arnd
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