[PATCH] btrfs: initialize location to fix -Wmaybe-uninitialized in btrfs_lookup_dentry()

[PATCH] btrfs: initialize location to fix -Wmaybe-uninitialized in btrfs_lookup_dentry()

[David Sterba]

Some arch + compiler combinations report a potentially unused variable
location in btrfs_lookup_dentry(). This is a false alert as the variable
is passed by value and always valid or there's an error. The compilers
cannot probably reason about that although btrfs_inode_by_name() is in
the same file.

   >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.objectid' may be used
   +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5603:9
   >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.type' may be used
   +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5674:5

   m68k-gcc8/m68k-allmodconfig
   mips-gcc8/mips-allmodconfig
   powerpc-gcc5/powerpc-all{mod,yes}config
   powerpc-gcc5/ppc64_defconfig

Initialize it to zero, this should fix the warnings and won't change the
behaviour as btrfs_inode_by_name() accepts only a root or inode item
types, otherwise returns an error.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/linux-btrfs/bd4e9928-17b3-9257-8ba7-6b7f9bbb639a@linux-m68k.org/
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 32010127710d..333b0e8587a2 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5667,7 +5667,7 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 	struct inode *inode;
 	struct btrfs_root *root = BTRFS_I(dir)->root;
 	struct btrfs_root *sub_root = root;
-	struct btrfs_key location;
+	struct btrfs_key location = { 0 };
 	u8 di_type = 0;
 	int ret = 0;
 
-- 
2.45.0

Re: [PATCH] btrfs: initialize location to fix -Wmaybe-uninitialized in btrfs_lookup_dentry()

[Qu Wenruo]

在 2024/7/30 05:36, David Sterba 写道:
> Some arch + compiler combinations report a potentially unused variable
> location in btrfs_lookup_dentry(). This is a false alert as the variable
> is passed by value and always valid or there's an error. The compilers
> cannot probably reason about that although btrfs_inode_by_name() is in
> the same file.
>
>     >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.objectid' may be used
>     +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5603:9
>     >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.type' may be used
>     +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5674:5
>
>     m68k-gcc8/m68k-allmodconfig
>     mips-gcc8/mips-allmodconfig
>     powerpc-gcc5/powerpc-all{mod,yes}config
>     powerpc-gcc5/ppc64_defconfig
>
> Initialize it to zero, this should fix the warnings and won't change the
> behaviour as btrfs_inode_by_name() accepts only a root or inode item
> types, otherwise returns an error.
>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Link: https://lore.kernel.org/linux-btrfs/bd4e9928-17b3-9257-8ba7-6b7f9bbb639a@linux-m68k.org/
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Although I hate to update our code for bad compilers, I guess it's
unavoidable anyway.

Thanks,
Qu
> ---
>   fs/btrfs/inode.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 32010127710d..333b0e8587a2 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5667,7 +5667,7 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
>   	struct inode *inode;
>   	struct btrfs_root *root = BTRFS_I(dir)->root;
>   	struct btrfs_root *sub_root = root;
> -	struct btrfs_key location;
> +	struct btrfs_key location = { 0 };
>   	u8 di_type = 0;
>   	int ret = 0;
>

Re: [PATCH] btrfs: initialize location to fix -Wmaybe-uninitialized in btrfs_lookup_dentry()

[David Sterba]

On Tue, Jul 30, 2024 at 07:04:36AM +0930, Qu Wenruo wrote:
> 
> 
> 在 2024/7/30 05:36, David Sterba 写道:
> > Some arch + compiler combinations report a potentially unused variable
> > location in btrfs_lookup_dentry(). This is a false alert as the variable
> > is passed by value and always valid or there's an error. The compilers
> > cannot probably reason about that although btrfs_inode_by_name() is in
> > the same file.
> >
> >     >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.objectid' may be used
> >     +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5603:9
> >     >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.type' may be used
> >     +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5674:5
> >
> >     m68k-gcc8/m68k-allmodconfig
> >     mips-gcc8/mips-allmodconfig
> >     powerpc-gcc5/powerpc-all{mod,yes}config
> >     powerpc-gcc5/ppc64_defconfig
> >
> > Initialize it to zero, this should fix the warnings and won't change the
> > behaviour as btrfs_inode_by_name() accepts only a root or inode item
> > types, otherwise returns an error.
> >
> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > Link: https://lore.kernel.org/linux-btrfs/bd4e9928-17b3-9257-8ba7-6b7f9bbb639a@linux-m68k.org/
> > Signed-off-by: David Sterba <dsterba@suse.com>
> 
> Reviewed-by: Qu Wenruo <wqu@suse.com>
> 
> Although I hate to update our code for bad compilers, I guess it's
> unavoidable anyway.

Yeah, but the number of such fixups is bearable, we have added like one
per release.

Re: [PATCH] btrfs: initialize location to fix -Wmaybe-uninitialized in btrfs_lookup_dentry()

[Geert Uytterhoeven]

Hi David,

On Mon, Jul 29, 2024 at 10:06 PM David Sterba <dsterba@suse.com> wrote:
> Some arch + compiler combinations report a potentially unused variable
> location in btrfs_lookup_dentry(). This is a false alert as the variable
> is passed by value and always valid or there's an error. The compilers
> cannot probably reason about that although btrfs_inode_by_name() is in
> the same file.
>
>    >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.objectid' may be used
>    +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5603:9
>    >  + /kisskb/src/fs/btrfs/inode.c: error: 'location.type' may be used
>    +uninitialized in this function [-Werror=maybe-uninitialized]:  => 5674:5
>
>    m68k-gcc8/m68k-allmodconfig
>    mips-gcc8/mips-allmodconfig
>    powerpc-gcc5/powerpc-all{mod,yes}config
>    powerpc-gcc5/ppc64_defconfig
>
> Initialize it to zero, this should fix the warnings and won't change the
> behaviour as btrfs_inode_by_name() accepts only a root or inode item
> types, otherwise returns an error.
>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Link: https://lore.kernel.org/linux-btrfs/bd4e9928-17b3-9257-8ba7-6b7f9bbb639a@linux-m68k.org/
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 32010127710d..333b0e8587a2 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5667,7 +5667,7 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
>         struct inode *inode;
>         struct btrfs_root *root = BTRFS_I(dir)->root;
>         struct btrfs_root *sub_root = root;
> -       struct btrfs_key location;
> +       struct btrfs_key location = { 0 };
>         u8 di_type = 0;
>         int ret = 0;
>

Thanks, this gets rid of the failure for m68k/allmodconfig
(gcc version 8.4.0 (Ubuntu 8.4.0-3ubuntu1) and 9.5.0 (Ubuntu
9.5.0-1ubuntu1~22.04)).

On m68k, it didn't show up with gcc 10, 11, and 12.
Also, enabling CONFIG_CC_OPTIMIZE_FOR_SIZE fixed it for gcc 8/9.

Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds