Re: [PATCH v3 REBASED 0/3] btrfs: fix issues due to alien device

[Nikolay Borisov <nborisov@suse.com>]

On 28.04.20 г. 18:22 ч., Anand Jain wrote:
> v3 REBASED: Based on the latest misc-next. for for-5.8.
>    Dropped the following patches as there were concerns about the usage
>    of error code -EUCLEAN
> 	btrfs: remove identified alien device in open_fs_devices
> 	btrfs: remove identified alien btrfs device in open_fs_devices
> 
>    Rmaining 3 patches here have obtained reviewed-by. With this pathset
>    the pertaining fstests btrfs/197 and btrfs/198 (which tests 3 bugs)
>    would pass as the patch 2/3 fixed a bug and 3/3 fixed the trigger
>    of 2 other bugs (patch 1/3 is just a cleanup). Further at the moment
>    I am not sure if there is any other trigger where it could again leave
>    an alien device in the fs_devices leading to the same/similar bugs.
> 
> ==== original email ====
> v3: Fix alien device is due to wipefs in Patch4.
>     Fix a nit in Patch3.
>     Patches are reordered.
> 
> Alien device is a device in fs_devices list having a different fsid than
> the expected fsid or no btrfs_magic. This patch set fixes issues found due
> to the same.
> 
> Patch1: is a cleanup patch, not related.
> Patch2: fixes failing to mount a degraded RAIDs (RAID1/5/6/10), by
> 	hardening the function btrfs_free_extra_devids().
> Patch3: fixes the missing device (due to alien btrfs-device) not missing in
> 	the userland, by hardening the function btrfs_open_one_device().
> Patch4: fixes the missing device (due to alien device) not missing in
> 	the userland, by returning EUCLEAN in btrfs_read_dev_one_super().
> Patch5: eliminates the source of the alien device in the fs_devices.
> 
> PS: Fundamentally its wrong approach that btrfs-progs deduces the device
> missing state in the userland instead of obtaining it from the kernel.
> I remember objecting on the btrfs-progs patch which did that, but still
> it got merged, bugs in p3 and p4 are its side effects. I wrote
> patches to read device_state from the kernel using ioctl, procfs and
> sysfs but it didn't get the due attention till a merger.
> 
> Anand Jain (3):
>   btrfs: drop useless goto in open_fs_devices
>   btrfs: include non-missing as a qualifier for the latest_bdev
>   btrfs: free alien device due to device add
> 
>  fs/btrfs/volumes.c | 30 ++++++++++++++++++++++--------
>  1 file changed, 22 insertions(+), 8 deletions(-)
> 


One thing I'm not clear is how can we get into a situation of an alien
device. I.e devices should be in fs_devices iff they are part of the
filesystem, no ?