On Sat, 10 Jun 2017, Kai Krakow wrote:

Am Fri, 9 Jun 2017 01:46:24 +0000 (UTC)
schrieb Eric Wheeler [off-list ref]:

quoted

On Fri, 2 Jun 2017, feng D wrote:

quoted

hi:

Some time, the online machine will appear disk gone situation,
although this is not very common, but we have too many machines, so
still will encounter it.

That in the case of disk gone, /sys/block/bcache0/bcache/stop is
not found, this case how to delete the bcache0?  

An interesting question.  Is it still available from the cache device
in /sys/fs/bcache/* somewhere?  I'm guessing not, but check.

Do you have a procedure to reproduce this problem
where /sys/block/bcache0 has been hotplugged into oblivion?

You easily run into the same situation when you stop the device instead
of detaching it. Bcache then doesn't release its cache device and
cannot be stopped/unregistered, because every interface for shutting
bcache down has vanished: It can only be reached through the backing
devices but the bcache interface below those is gone.

I think bcache needs a way to force unregister the cache device...
Otherwise the cache device stays busy and cannot be registered, neither
can any devices be attached again in this state.

I'm having trouble reproducing:

]# echo /dev/centos/bcache0 > /sys/fs/bcache/register
]# echo /dev/centos/bcache0-cache > /sys/fs/bcache/register
]# 
]# echo 1 > /sys/block/bcache0/bcache/stop
]# echo 1 > /sys/fs/bcache/3e57bc2e-4f01-4164-9b6d-54ef288ae394/stop
]#
]# echo /dev/centos/bcache0 > /sys/fs/bcache/register
]# echo /dev/centos/bcache0-cache > /sys/fs/bcache/register

also tried swapping the stop order:

]# echo /dev/centos/bcache0 > /sys/fs/bcache/register
]# echo /dev/centos/bcache0-cache > /sys/fs/bcache/register
]#
]# echo 1 > /sys/fs/bcache/3e57bc2e-4f01-4164-9b6d-54ef288ae394/stop   
]# echo 1 > /sys/block/bcache0/bcache/stop 
   >>> fails, no such file, but re-registers fine below
]#
]# echo /dev/centos/bcache0 > /sys/fs/bcache/register
]# echo /dev/centos/bcache0-cache > /sys/fs/bcache/register

What am I missing here?


--
Eric Wheeler

-- 
Regards,
Kai

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