Re: BUG: drivers/md/bcache/writeback.c:237

On Thu, 25 Feb 2016, Marc MERLIN wrote:

On Thu, Feb 25, 2016 at 06:18:03PM +0800, Zhu Yanhai wrote:

quoted

Marc,
When did you *first* see this BUG_ON? During boot up or far after the
whole system is up?

I setup bcache, had it work a bit.
During shutdown, it crapped out when syncing/unmounting

Do you have more information about what crapped out on shutdown?  
   Memory?
   IO Error?
   Just hung so the reset button was pushed?

Was there a backtrace?

It might be a good idea to use netconsole and point it at a syslog 
server to catch the whole backtrace.

After each subsequent boot, the system crashed as soon as the module loaded
and scanned my disks.

So just to clarify, the current BUG_ON discussed is happening at boot, and 
is not the mid-shutdown error that first happened?

-Eric

While I understand I did hit a bug, I've been on a cruisade to get BUG_ON
removed from btrfs code and replaced with warns/abort/remount read only.
On a production system, BUG_ON really sucks, especially if it happens as
soon as the kernel loads and before you can even do anything to fix the
issue :)

If there is any chance this can be changed into some kind of abort that
disables bcache or just prevents bcache from making damaging writes to the
backing device, by simply disabling the cache, that would be much better :)

In the meantime, I've stopped using writeback since it seems that it's been
the reason why I hit this problem.

Thanks,
Marc
-- 
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Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/