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From: Andreas Dilger <adilger@dilger.ca>
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Subject: =?utf-8?Q?Re=3A_=5BPATCH=5D_ext4=3A_extents=3A_Remove_unnecessary?=
 =?utf-8?Q?_=E2=80=98NULL=E2=80=99_values_from_ablocks?=
Date: Mon, 8 Apr 2024 14:51:23 -0600
In-Reply-To: <20240402024804.29411-1-zeming@nfschina.com>
Cc: Theodore Ts'o <tytso@mit.edu>,
 Ext4 Developers List <linux-ext4@vger.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To: Li zeming <zeming@nfschina.com>
References: <20240402024804.29411-1-zeming@nfschina.com>


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On Apr 1, 2024, at 8:48 PM, Li zeming <zeming@nfschina.com> wrote:
>=20
> ablocks is assigned first, so it does not need to initialize the
> assignment.

While it is true that "ablocks" is currently set before use,
this is happening a long way away from the variable declaration
and also "ablocks" is used after the "cleanup:" label error case:

cleanup:
        if (bh) {
                if (buffer_locked(bh))
                        unlock_buffer(bh);
                brelse(bh);
        }

        if (err) {
                /* free all allocated blocks in error case */
                for (i =3D 0; i < depth; i++) {
                        if (!ablocks[i])
                                continue;
                        ext4_free_blocks(handle, inode, NULL, =
ablocks[i], 1,
                                         EXT4_FREE_BLOCKS_METADATA);
                }
        }
        kfree(ablocks);

So there is definitely a risk that a code change in the future
would introduce hard-to-debug problems, crashes, or even just
spurious static code analysis warnings.  My recommendation would
be to keep this 1-cycle local variable initialization in place
rather than spend hours or days trying to debug and fix a crash
here in the future.

Cheers, Andreas

>=20
> Signed-off-by: Li zeming <zeming@nfschina.com>
> ---
> fs/ext4/extents.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 4ab96f01a6f31..caace8c3fd3c1 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -1061,7 +1061,7 @@ static int ext4_ext_split(handle_t *handle, =
struct inode *inode,
> 	int i =3D at, k, m, a;
> 	ext4_fsblk_t newblock, oldblock;
> 	__le32 border;
> -	ext4_fsblk_t *ablocks =3D NULL; /* array of allocated blocks */
> +	ext4_fsblk_t *ablocks; /* array of allocated blocks */
> 	gfp_t gfp_flags =3D GFP_NOFS;
> 	int err =3D 0;
> 	size_t ext_size =3D 0;
> --
> 2.18.2
>=20


Cheers, Andreas


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