Re: [f2fs-dev] [bug report] compiler warning: fs/f2fs/node.c: In function ‘__set_nat_cache_dirty’: ‘head’ may be used uninitialized

[Chao Yu <yuchao0@huawei.com>]

On 2019/10/24 17:54, Ardelean, Alexandru wrote:
> On Thu, 2019-10-24 at 17:12 +0800, Chao Yu wrote:
>> [External]
>>
>> On 2019/10/23 22:02, Ardelean, Alexandru wrote:
>>> Seems to have been introduced via:
>>>
>>> ----------------------------------------------------------------
>>>
>>> commit 780de47cf6cb5f524cd98ec8ffbffc3da5696e17
>>> Author: Chao Yu <yuchao0@huawei.com>
>>> Date:   Tue Mar 20 23:08:30 2018 +0800
>>>
>>>     f2fs: don't track new nat entry in nat set
>>>     
>>>     Nat entry set is used only in checkpoint(), and during checkpoint()
>>> we
>>>     won't flush new nat entry with unallocated address, so we don't
>>> need to
>>>     add new nat entry into nat set, then nat_entry_set::entry_cnt can
>>>     indicate actual entry count we need to flush in checkpoint().
>>>     
>>>     Signed-off-by: Yunlei He <heyunlei@huawei.com>
>>>     Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>     Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>> ----------------------------------------------------------------
>>>
>>> Compiler warning is:
>>> ----------------------------------------------------------------
>>>
>>>   CC      fs/f2fs/node.o
>>> In file included from ./include/linux/wait.h:7:0,
>>>                  from ./include/linux/wait_bit.h:8,
>>>                  from ./include/linux/fs.h:6,
>>>                  from fs/f2fs/node.c:11:
>>> fs/f2fs/node.c: In function ‘__set_nat_cache_dirty’:
>>> ./include/linux/list.h:63:13: error: ‘head’ may be used uninitialized
>>> in
>>> this function [-Werror=maybe-uninitialized]
>>>   next->prev = new;
>>>              ^
>>> fs/f2fs/node.c:238:24: note: ‘head’ was declared here
>>>   struct nat_entry_set *head;
>>
>> That's not correct, @head will only be assigned and used if new_ne equals
>> NULL.
> 
> Ack.
> I admit that I don't understand the code, and don't claim to understand it.
> 
> This may be just a weird compiler issue.
> I thought I'd send it just as a heads-up.

I think that's the right thing to do.

> I saw this on a Raspberry Pi branch [after we enabled warnings as errors]:
> https://travis-ci.org/analogdevicesinc/linux/jobs/601844926#L1208
> 
> Looking in the latest f2fs/dev[-test] tree, it looks like the code is
> similar as in 4.19.
> https://github.com/analogdevicesinc/linux/blob/rpi-4.19.y/fs/f2fs/node.c#L235
> 
> Could be that the RPi branch has some more compiler-stuff enabled.
> 
> In any case, feel free to disregard this.
> We will see how we fix this on our end for that branch specifically.

That would make sense, let me know if you have any other suspicious compiler
warnings. :)

Thanks,

> 
> Thanks
> Alex
> 
>>
>> Thanks,
>>
>>>                         ^
>>> cc1: all warnings being treated as errors
>>> ----------------------------------------------------------------
>>>
>>> Thanks
>>> Alex
>>>
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