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

[Anand Jain <anand.jain@oracle.com>]

On 12/2/19 7:23 PM, Filipe Manana wrote:
> 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...

  Nope. I didn't go that deep.

> 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.

  Makes sense. Will send v2 with it.

Thanks, Anand

> 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
>>
> 
>