[ Re-send to both linux-block and linux-bcache ]

Hi,

A few days ago, my system refused to boot because it couldn't find the root 
filesystem anymore. The root filesystem is ext4 on LVM on dm-crypt on bcache, 
using kernel 4.9.92 (from Debian stretch). Booting from a recovery medium with 
Kernel 4.16, I got:

[   84.551715] bcache: register_bcache() error /dev/sda4: device already 
registered
[   84.553188] bcache: register_bcache() error /dev/sdc2: device already 
registered
[   84.616438] bcache: error on 1330b5f6-0c13-43ec-b925-2ee2734b135f:
[   84.616440] bad btree header at bucket 85065, block 0, 0 keys
[   84.616442] , disabling caching
[   84.616445] bcache: register_cache() registered cache device sdb2
[   84.616597] bcache: cache_set_free() Cache set 
1330b5f6-0c13-43ec-b925-2ee2734b135f unregistered
[   85.375933]  sdb: sdb1 sdb2 sdb4 < sdb5 >
[   85.416610] bcache: error on 1330b5f6-0c13-43ec-b925-2ee2734b135f:
[   85.416612] bad btree header at bucket 85065, block 0, 0 keys
[   85.416614] , disabling caching
[   85.416618] bcache: register_cache() registered cache device sdb2
[   85.416624] bcache: register_bcache() error /dev/sdc2: device already 
registered
[   85.416626] bcache: register_bcache() error /dev/sda4: device already 
registered
[   85.416796] bcache: cache_set_free() Cache set 
1330b5f6-0c13-43ec-b925-2ee2734b135f unregistered
[   85.488246] bcache: error on 1330b5f6-0c13-43ec-b925-2ee2734b135f:
[   85.488249] bad btree header at bucket 85065, block 0, 0 keys
[   85.488251] , disabling caching
[   85.488254] bcache: register_cache() registered cache device sdb2
[   85.488429] bcache: cache_set_free() Cache set 
1330b5f6-0c13-43ec-b925-2ee2734b135f unregistered
[   85.560003] bcache: error on 1330b5f6-0c13-43ec-b925-2ee2734b135f:
[   85.560006] bad btree header at bucket 85065, block 0, 0 keys
[   85.560008] , disabling caching
[   85.560013] bcache: register_cache() registered cache device sdb2
[   85.560017] bcache: register_bcache() error /dev/sda4: device already 
registered
[   85.560217] bcache: cache_set_free() Cache set 
1330b5f6-0c13-43ec-b925-2ee2734b135f unregistered
[   85.571950] bcache: register_bcache() error /dev/sdc2: device already 
registered
[   85.580628] bcache: register_bcache() error /dev/sdc2: device already 
registered
[   85.761969] bcache: register_bcache() error /dev/sda4: device already 
registered
[   85.792749] bcache: register_bcache() error /dev/sda4: device already 
registered
[   85.952931] bcache: register_bcache() error /dev/sda4: device already 
registered
[   85.955640] bcache: register_bcache() error /dev/sda4: device already 
registered
[...]

These are the first messages that mention bcache. Note that the first message 
is that the device is already registered - is that normal?

smartctl does not report any errors on backing or caching disks, and the system 
was shutdown cleanly.

The only possibly related thing that comes to mind is that a few days ago I 
hibernated and resumed the system (this is something I normally don't do). 
Resume worked fine as far as I could tell though, and there have been no 
unclean shutdowns.

Is there a way to narrow down what may have caused this corruption?

And, is there a way to gracefully recover from this situation without wiping 
everything? Since the message mentions only problems with one block, can I 
maybe tell bcache to just ignore/drop this specific block?

Thanks!
-Nikolaus
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