Re: Mount/df/PAM login hangs during rsync to btrfs subvolume, or maybe doing btrfs subvolume snapshot

[Nikolay Borisov <nborisov@suse.com>]

On 12.09.19 г. 7:38 ч., David Newall wrote:
> On 11/9/19 8:22 pm, Nikolay Borisov wrote:
>>> I saved it tohttps://davidnewall.com/kern.1
>> Nothing useful in that log, everything seems normal.
> 
> Thank you, again, for your help.  I am grateful.
> 
> If I understand the output, both df and mount are waiting for
> show_mountinfo which is waiting for btrfs_show_devname which is waiting
> to get a lock.  They have to wait to find the devname for ten minutes. 
> Is that really normal?

It's normal for them to wait for the lock, it's not normal for the lock
to be taken for 10 minutes.

> 
> I'm not saying that btrfs is behind it, but it does seem like something
> is not right.

From my POV what's wrong is the fact that btrfs transaction commit is
taking a long time. Is it possible that the underlying storage is
exhibiting problems e.g. a dying disk/ssd?

> 
> I notice that there's a waiting btrfs-transation, too.  I don't know
> what the transaction would be, and no doubt it's completely appropriate,
> even though the use of btrfs at that point is merely one mount (and one
> mount of ext2 over a sub-directory, probably no involvement by btrfs.)
> 
> I see, too, that systemd is waiting for btrfs_show_devname.  It's a
> pattern.
> 
> I take your point about the kernel being somewhat old and accept that
> I'm unlikely to get far without confirming the problem on a recent kernel.
> 
>