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

["Ardelean, Alexandru" <alexandru.Ardelean@analog.com>]

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 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.

Thanks
Alex

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