Re: [PATCH] btrfs: fix warn_on for send from readonly mount

[Filipe Manana <fdmanana@gmail.com>]

On Mon, Dec 2, 2019 at 9:46 AM Anand Jain <anand.jain@oracle.com> wrote:
>
> We log warning if root::orphan_cleanup_state is not set to
> ORPHAN_CLEANUP_DONE in btrfs_ioctl_send(). However if the filesystem is
> mounted as readonly we skip the orphan items cleanup during the lookup
> and root::orphan_cleanup_state remains at the init state 0 instead of
> ORPHAN_CLEANUP_DONE (2).
>
> WARNING: CPU: 0 PID: 2616 at /Volumes/ws/btrfs-devel/fs/btrfs/send.c:7090 btrfs_ioctl_send+0xb2f/0x18c0 [btrfs]
> ::
> RIP: 0010:btrfs_ioctl_send+0xb2f/0x18c0 [btrfs]
> ::
> Call Trace:
> ::
> _btrfs_ioctl_send+0x7b/0x110 [btrfs]
> btrfs_ioctl+0x150a/0x2b00 [btrfs]
> ::
> do_vfs_ioctl+0xa9/0x620
> ? __fget+0xac/0xe0
> ksys_ioctl+0x60/0x90
> __x64_sys_ioctl+0x16/0x20
> do_syscall_64+0x49/0x130
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reproducer:
>   mkfs.btrfs -fq /dev/sdb && mount /dev/sdb /btrfs
>   btrfs subvolume create /btrfs/sv1
>   btrfs subvolume snapshot -r /btrfs/sv1 /btrfs/ss1
>   umount /btrfs && mount -o ro /dev/sdb /btrfs
>   btrfs send /btrfs/ss1 -f /tmp/f
>
> Fix this by checking for the expected ORPHAN_CLEANUP_DONE only if the
> filesystem is in writable state.

I wonder if you know why the warning is there in the first place...

In my opinion we could remove the warning completely because:

1) Having orphan items means we could have files to delete (link count
of 0) and dealing with such cases could make send fail for several
reasons.
    If this happens, it's not longer a problem since the following commit:

    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=46b2f4590aab71d31088a265c86026b1e96c9de4

2) Orphan items used to indicate previously unfinished truncations, in
which case it would lead to send creating corrupt files at the
destination (i_size incorrect and the file filled with zeroes between
real i_size and stale i_size).
    We no longer need to create orphans for truncations since commit:

    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f7e9e8fc792fe2f823ff7d64d23f4363b3f2203a

I think that information needs to be in the changelog. And, as said
before, I think the warning could go away completely.

Thanks.

>
> Reported-by: Christoph Anton Mitterer <calestyo@scientia.net>
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/send.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index ae2db5eb1549..e3acec8aa8de 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -7085,9 +7085,11 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
>
>         /*
>          * This is done when we lookup the root, it should already be complete
> -        * by the time we get here.
> +        * by the time we get here, unless the filesystem is readonly where the
> +        * orphan_cleanup_state is never started.
>          */
> -       WARN_ON(send_root->orphan_cleanup_state != ORPHAN_CLEANUP_DONE);
> +       if (!sb_rdonly(file_inode(mnt_file)->i_sb))
> +               WARN_ON(send_root->orphan_cleanup_state != ORPHAN_CLEANUP_DONE);
>
>         /*
>          * Userspace tools do the checks and warn the user if it's
> --
> 2.23.0
>


-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”