On Wed, Mar 16, 2022 at 03:57:32PM +0000, Filipe Manana wrote:
> On Wed, Mar 16, 2022 at 10:22:37PM +0900, Naohiro Aota wrote:
> > When btrfs balance is interrupted with umount, the background balance
> > resumes on the next mount. There is a potential deadlock with FS freezing
> > here like as described in commit 26559780b953 ("btrfs: zoned: mark
> > relocation as writing").
> >
> > Mark the process as sb_writing. To preserve the order of sb_start_write()
> > (or mnt_want_write_file()) and btrfs_exclop_start(), call sb_start_write()
> > at btrfs_resume_balance_async() before taking fs_info->super_lock.
>
> This paragraph is now outdated, it should go away as it applied only to v1.
> The ordering problem is no longer relevant and we don't do anything at
> btrfs_resume_balance_async() anymore.
Oops. I took the last sentence and unified it with the first paragraph.
> >
> > Cc: stable@xxxxxxxxxxxxxxx # 4.9+
> > Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
>
> Other than that, it looks good.
>
> Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Thanks.
> Thanks.
>
> > ---
> > fs/btrfs/volumes.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index 3fd17e87815a..3471698fd831 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -4430,10 +4430,12 @@ static int balance_kthread(void *data)
> > struct btrfs_fs_info *fs_info = data;
> > int ret = 0;
> >
> > + sb_start_write(fs_info->sb);
> > mutex_lock(&fs_info->balance_mutex);
> > if (fs_info->balance_ctl)
> > ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
> > mutex_unlock(&fs_info->balance_mutex);
> > + sb_end_write(fs_info->sb);
> >
> > return ret;
> > }
> > --
> > 2.35.1
> >
