linux-kernel - Re: linux-next: build warning after merge of the pstore tree

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Date:   Tue, 15 Nov 2016 21:19:43 -0800
From:   Joel Fernandes <joelaf@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next <linux-next@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of the pstore tree

On Tue, Nov 15, 2016 at 4:35 PM, Kees Cook <keescook@...omium.org> wrote:
> On Tue, Nov 15, 2016 at 4:27 PM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>> Hi Kees,
>>
>> After merging the pstore tree, today's linux-next build (x86_64
>> allmodconfig) produced this warning:
>>
>> In file included from include/linux/rcupdate.h:38:0,
>>                  from include/linux/idr.h:18,
>>                  from include/linux/kernfs.h:14,
>>                  from include/linux/sysfs.h:15,
>>                  from include/linux/kobject.h:21,
>>                  from include/linux/device.h:17,
>>                  from fs/pstore/ram_core.c:17:
>> fs/pstore/ram_core.c: In function 'buffer_size_add':
>> include/linux/spinlock.h:246:3: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>    _raw_spin_unlock_irqrestore(lock, flags); \
>>    ^
>> fs/pstore/ram_core.c:78:16: note: 'flags' was declared here
>>   unsigned long flags;
>>                 ^
>> In file included from include/linux/rcupdate.h:38:0,
>>                  from include/linux/idr.h:18,
>>                  from include/linux/kernfs.h:14,
>>                  from include/linux/sysfs.h:15,
>>                  from include/linux/kobject.h:21,
>>                  from include/linux/device.h:17,
>>                  from fs/pstore/ram_core.c:17:
>> fs/pstore/ram_core.c: In function 'buffer_start_add':
>> include/linux/spinlock.h:246:3: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>    _raw_spin_unlock_irqrestore(lock, flags); \
>>    ^
>> fs/pstore/ram_core.c:56:16: note: 'flags' was declared here
>>   unsigned long flags;
>>                 ^
>>
>> Introduced by commit
>>
>>   95937ddce59a ("pstore: Allow prz to control need for locking")
>>
>> They appear to be a very noisy false positives. :-(
>
> Hah. Ironically, I ran sparse against this code to make sure it would
> be happy with the conditional locking, and totally missed the flags
> bit. I'll switch it to explicitly initialize flags to silence this.
>

Ah! False positive.

Thanks a lot Kees for fixing it.

Regards,
Joel