linux-kernel - Re: stable/linux-3.16.y build: 178 builds: 1 failed, 177 passed, 2 errors, 57 warnings (v3.16.52)

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Message-ID: <0ecf39a8-dfc1-e895-ad6b-e2cf21a30e01@colorfullife.com>
Date:   Sat, 13 Jan 2018 19:51:06 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Arnd Bergmann <arnd@...db.de>,
        "kernelci.org bot" <bot@...nelci.org>
Cc:     Kernel Build Reports Mailman List 
        <kernel-build-reports@...ts.linaro.org>,
        "3.16.x" <stable@...r.kernel.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: stable/linux-3.16.y build: 178 builds: 1 failed, 177 passed, 2
 errors, 57 warnings (v3.16.52)

Hi Arnd,

On 01/03/2018 12:15 AM, Arnd Bergmann wrote:
>
>> 2 ipc/sem.c:377:6: warning: '___p1' may be used uninitialized in this function [-Wmaybe-uninitialized]
> This code was last touched in 3.16 by the backport of commit
> 5864a2fd3088 ("ipc/sem.c: fix complex_count vs. simple op race")
>
> The warning is in "smp_load_acquire(&sma->complex_mode))", and I suspect
> that commit 27d7be1801a4 ("ipc/sem.c: avoid using spin_unlock_wait()")
> avoided the warning upstream by removing the smp_mb() before it.
The smp_mb() pairs with spin_unlock_wait() in complexmode_enter()
It is removed by commit 27d7be1801a4 ("ipc/sem.c: avoid using 
spin_unlock_wait()").

 From what I see, it doesn't exist in any of the stable kernels 
(intentionally, the above commit is a rewrite for better performance).

___p1 is from smp_load_acquire()
 >        typeof(*p) ___p1 = READ_ONCE(*p);                               \

I don't see how ___p1 could be used uninitialized. Perhaps a compiler issue?

--
     Manfred