On Wed, 3 Aug 2016, Marc MERLIN wrote:

This happens on all kernels up to 4.7.
Sorry, it happens earlier than ethernet coming up or my storage, so I can't
use netconsole or other text dumps:
https://goo.gl/photos/ubsi6maZXsjkevYY7

Looks like the warning happens on the registration of one of my bcache, but
I can't tell which one or why.

Does the trace give any hints?
(please ignore the load modules errors below, different issue)

Does it cause a problem, or just warn?

 73 uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
 74 {
 75         uint8_t ret = ++b->gen;
 76 
 77         ca->set->need_gc = max(ca->set->need_gc, bucket_gc_gen(b));
 78         WARN_ON_ONCE(ca->set->need_gc > BUCKET_GC_GEN_MAX);
 79 
 80         return ret;
 81 }

It looks like something needs garbage collected but perhaps isn't.  

You could write to sysfs/.../trigger_gc:
 
https://evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt
	trigger_gc
	  Writing to this file forces garbage collection to run.

If that doesn't work, I wonder what increasing BUCKET_GC_GEN_MAX would do, 
though I don't know if that is safe.  Its set to 96U, so its not on on a 
bit boundary which sounds like it could be slightly safer---but I wouldn't 
try it unless this is a test machine.


--
Eric Wheeler

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/  
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