On Thu, Mar 03, 2016 at 04:17:24AM +0000, Eric Wheeler wrote:

On Fri, 26 Feb 2016, Eric Wheeler wrote:

quoted

On Fri, 26 Feb 2016, Marc MERLIN wrote:

quoted

On Fri, Feb 26, 2016 at 04:55:02AM +0000, Eric Wheeler wrote:

quoted

According to Documentation/bcache.txt:
	"" If you're booting up and your cache device is gone and never
	coming back, you can force run the backing device:
	  echo 1 > /sys/block/sdb/bcache/running
	[...]
	The backing device will still use that cache set if it shows up
	in the future, but all the cached data will be invalidated.  ""

So it seems that you are safe.  (It would be interesting to know how it 
invalidates the cache.  Maybe bumps the Set UUID?  Not sure.)

 
Yeah, that was  my understanding too, but I wanted to make sure.
Strangely (worringly so?) the cache was replayed at boot, and this time
nothing crashed, or any traceback.
Now I'm wondering if it pushed garbage onto my filesystem :-/

I'm not convinced that journal replay will writeback, especially because 
of the documentation stating that forcing a bdev into a running state 
invalidates its cache.  I think it just keeps the datastructures in good 
shape on the cachedev, even though the cachedev was invalidated by forcing 
a 'running' state.

 
Hi Marc,

Thank you for your help investigating.  The two patches resulting from our 
testing are on their way into 4.5.

 
I saw that, thank you.

How has it been running since?  Any new backtraces to investigate?

No crashes since then, although my last one started when I was shutting
the laptop down, and I don't shut down very often (actually virtually
never unless I upgrade kernels :) ).

But that's another way ot say so far so good :)

Thanks for your work looking into this.
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/                         | PGP 1024R/763BE901