Heads up..
If there are people playing with 3.17 and btrfs at the moment then you'll want this patch, pull request for Linus below (not yet merged into the mainline so not yet a candidate for a stable release). The actual commit has a better description of the problem.
https://git.kernel.org/cgit/linux/kernel/git/mason/linux- btrfs.git/commit/?h=for- linus&id=529c9ab761315fb5bccc79176d270fd6392a8f07
Thanks for that. I think that's likely what bit me (or else there is some other unknown bug...) I was testing out 3.17-rc5 debian package as 3.16 has a bunch of bcache bugs (annoyances really - system load always >= bcache volumes) Looks like this patch missed 3.17.1. Better wait for 3.17.2 I guess... and then maybe wait some more to let others test with their data ;) James