On Sat, Aug 29, 2015 at 9:23 PM, Kenneth Lakin [off-list ref] wrote:

Hey. It looks like I'm being bitten by:
http://article.gmane.org/gmane.comp.file-systems.btrfs/44987/ except I'm
hitting it during rename, rather than unlink. Dmesg spew here:
http://pastebin.ca/3137198 (That pastebin post includes the -unrelated-
source of the W taint.)

I'm running on Gentoo hardened-sources 4.1.6 on x86 (rather than amd64).
The affected volume is mounted with
"rw,relatime,ssd,discard,space_cache,autodefrag" and -AFAIK- has no
subvolumes.

emerge is the blocked program and is the Gentoo package manager. This
lockup happens occasionally during the "Updating Portage cache" step of
the emerge sync operation. The emerge task is unkillable and is blocked
in D status. Attempts to re-run the cache update task have it hang at
what appears to be the same place. Only a reboot can "fix" the problem.
The rest of the system works just fine; the only thing that appears to
be blocked is the Portage cache update.

I couldn't find an open bug for this, but my Google-fu may be weak
today. Did I miss the bug report, or is this a currently unknown or
unconfirmed issue? Let me know if I can help with diagnostics.

The fix landed in 4.2-rc:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ca0709756710c47ec604dd08b9fc45929d36390

And it's not in 4.1 nor any other older releases.

-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."