Re: [PATCH v3] btrfs: fix warn_on for send from readonly mount

Filipe Manana
2019-12-05T11:43:51Z

On Thu, Dec 5, 2019 at 11:39 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). So during send in btrfs_ioctl_send() we hit
> the warning as below.
>
> WARN_ON(send_root->orphan_cleanup_state != ORPHAN_CLEANUP_DONE);
>
> 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
>
> The warning exists because having orphan inodes could confuse send
> and cause it to fail or produce incorrect streams.
> The two cases that would cause such send failures, which are already
> fixed are:
>
> 1) Inodes that were unlinked - these are orphanized and remain with a link
> count of 0. These caused send operations to fail because it expected to
> always find at least one path for an inode. However this is no longer a
> problem since send is now able to deal with such inodes since commit
> 46b2f4590aab ("Btrfs: fix send failure when root has deleted files still
> open") and treats them as having been completely removed (the state after
> a orphan cleanup is performed).
>
> 2) Inodes that were in the process of being truncated. These resulted in
> send not knowing about the truncation and potentially issue write
> operations full of zeroes for the range from the new file size to the old
> file size. This is no longer a problem because we no longer create orphan
> items for truncation since commit f7e9e8fc792f ("Btrfs: stop creating
> orphan items for truncate").
>
> As such before these commits, the WARN_ON here provided a clue in case
> something went wrong. Instead of being a warning against the
> root::orphan_cleanup_state value, it could have been more accurate by
> checking if there were actually any orphan items, and then issue a warning
> only if any exists, but that would be more expensive to check. Since
> orphanized inodes no longer cause problems for send, just remove the warning.
>
> Reported-by: Christoph Anton Mitterer <calestyo@scientia.net>
> Link: https://lore.kernel.org/linux-btrfs/21cb5e8d059f6e1496a903fa7bfc0a297e2f5370.camel@scientia.net/
> Suggested-by: Filipe Manana <fdmanana@gmail.com>

s/gmail.com/suse.com/
(David can probably do that when he picks the patch)

Reviewed-by: Filipe Manana <fdmanana@suse.com>

Thanks

> [ Remove warn_on() part, and its reasoning ]
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
> v3: Commit log updated.
> v2: Remove WARN_ON() completely.
> fs/btrfs/send.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index ae2db5eb1549..091e5bc8c7ea 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -7084,12 +7084,6 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
> spin_unlock(&send_root->root_item_lock);
>
> /*
> - * This is done when we lookup the root, it should already be complete
> - * by the time we get here.
> - */
> - WARN_ON(send_root->orphan_cleanup_state != ORPHAN_CLEANUP_DONE);
> -
> - /*
> * Userspace tools do the checks and warn the user if it's
> * not RO.
> */
> --
> 1.8.3.1
>

--
Filipe David Manana,

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