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References: <20220621070224.1231039-1-zhangshida@kylinos.cn>
In-Reply-To: <20220621070224.1231039-1-zhangshida@kylinos.cn>
From:   Stephen Zhang <starzhangzsd@gmail.com>
Date:   Tue, 21 Jun 2022 15:12:57 +0800
Message-ID: <CANubcdVceGMyjKbBLyrWZ9jStjWOLgk8AT7_1UDkx8eEb9VgLw@mail.gmail.com>
Subject: Re: [PATCH v2] xfs: add check before calling xfs_mod_fdblocks
To:     djwong@kernel.org, dchinner@redhat.com
Cc:     zhangshida <zhangshida@kylinos.cn>, linux-kernel@vger.kernel.org,
        linux-xfs@vger.kernel.org
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Shida Zhang <starzhangzsd@gmail.com> =E4=BA=8E2022=E5=B9=B46=E6=9C=8821=E6=
=97=A5=E5=91=A8=E4=BA=8C 15:02=E5=86=99=E9=81=93=EF=BC=9A
>
> Checks are missing when delta equals 0 in __xfs_ag_resv_free() and
> __xfs_ag_resv_init().
>
> Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
> ---
>  Changes from v1:
>  -Add checks before calling xfs_mod_fdblocks instead.
>
>  fs/xfs/libxfs/xfs_ag_resv.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
> index fe94058d4e9e..c8fa032e4b00 100644
> --- a/fs/xfs/libxfs/xfs_ag_resv.c
> +++ b/fs/xfs/libxfs/xfs_ag_resv.c
> @@ -149,7 +149,12 @@ __xfs_ag_resv_free(
>                 oldresv =3D resv->ar_orig_reserved;
>         else
>                 oldresv =3D resv->ar_reserved;
> -       error =3D xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
> +
> +       if (oldresv)
> +               error =3D xfs_mod_fdblocks(pag->pag_mount, oldresv, true)=
;
> +       else
> +               error =3D 0;
> +
>         resv->ar_reserved =3D 0;
>         resv->ar_asked =3D 0;
>         resv->ar_orig_reserved =3D 0;
> @@ -215,8 +220,13 @@ __xfs_ag_resv_init(
>
>         if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
>                 error =3D -ENOSPC;
> -       else
> -               error =3D xfs_mod_fdblocks(mp, -(int64_t)hidden_space, tr=
ue);
> +       else {
> +               error =3D 0;
> +               if (hidden_space)
> +                       error =3D xfs_mod_fdblocks(mp, -(int64_t)hidden_s=
pace,
> +                                               true);
> +       }
> +
>         if (error) {
>                 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agn=
o,
>                                 error, _RET_IP_);
> --
> 2.25.1
>

And the code path that lead delta =3D 0 is shown below:

=3D> xfs_mod_freecounter+0x84/0x2b8
=3D> __xfs_ag_resv_free+0xc4/0x188
=3D> xfs_ag_resv_free+0x24/0x50
=3D> xfs_fs_unreserve_ag_blocks+0x40/0x160
=3D> xfs_mountfs+0x500/0x900
=3D> xfs_fs_fill_super+0x3d8/0x810
=3D> get_tree_bdev+0x164/0x258
=3D> xfs_fs_get_tree+0x20/0x30
=3D> vfs_get_tree+0x30/0xf8
=3D> path_mount+0x3c4/0xa58
=3D> do_mount+0x74/0x98

=3D> xfs_mod_freecounter+0x84/0x2b8
=3D> __xfs_ag_resv_init+0x64/0x1d0
=3D> xfs_ag_resv_init+0x108/0x1c8
=3D> xfs_fs_reserve_ag_blocks+0x4c/0x110
=3D> xfs_mountfs+0x57c/0x900
=3D> xfs_fs_fill_super+0x3d8/0x810
=3D> get_tree_bdev+0x164/0x258
=3D> xfs_fs_get_tree+0x20/0x30
=3D> vfs_get_tree+0x30/0xf8
=3D> path_mount+0x3c4/0xa58
=3D> do_mount+0x74/0x98