Re: F21 fails to mount root part, btrfs check: Couldn't open file system

[Kai Krakow <hurikhan77@gmail.com>]

Chris Murphy <lists@colorremedies.com> schrieb:

> On Tue, Mar 31, 2015 at 2:09 PM, Chris Murphy <lists@colorremedies.com>
> wrote:
> 
>> Well you have to rule that out before anyone on this list can really
>> help. Try booting Fedora 21 install media, and using smartctl -x on
>> the drive.
> 
> While you're at it, try to mount the Btrfs volume in question normally
> and report kernel messages. If mount fails, try it with -o recovery
> mount option, and also report kernel messages and whether that fails.

I had this happen, too, lately. It's quite often happening after an unclean 
shutdown (which currently quite often happend to me due to the xorg intel 
driver having GPU freezes). SysRq+W shows that the mount process is locked 
somewhere in the btrfs code path and won't quit if Ctrl+C'd...

Only way to fix it was to btrfs-zero-log. But it still took some reboots 
from initramfs until it successfully mounted again (I could mount it in 
initramfs right after zero-log but upon reboot it hung again though at a 
different stage probably).

So I guess there's some race on the one hand (happens from time to time non-
related to fixing it with zero-log), and a deadlock on the other hand after 
some unclean shutdowns (more or less random).

My setup is 3-device btrfs-mraid1-draid0 on bcache. Bcache wasn't involved 
in the backtrace of SysRq+W, however. Apparently I don't have a screenshot 
of it because my smart phone is currently fried...

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