Re: Need help mounting laptop corrupted root btrfs. Kernel BUG at fs/btrfs/volumes.c:3707

[Marc MERLIN <marc@merlins.org>]

If any devs want info out of my drive, please ask today, I really need to
fix it tomorrow.
I'll try btrfs-zero-log otherwise and if not, wipe and start over.

Marc

On Thu, Oct 25, 2012 at 12:58:05PM -0700, Marc MERLIN wrote:
> Howdy,
> 
> I can wait a day or maybe 2 before I have to wipe and restore from backup.
> Please let me know if you have a patch against 3.6.3 you'd like me to try
> to mount/recover this filesystem, or whether you'd like me to try btrfsck.
> 
> 
> My laptop had a problem with its boot drive which prevented linux
> from writing to it, and in turn caused btrfs to have incomplete writes 
> to it.
> After reboot, the boot drive was fine, but the btrfs filesystem has
> a corruption that prevents it from being mounted.
> 
> Unfortunately the mount crash prevents writing of crash data to even another
> drive since linux stops before the crash data can be written to syslog.
> 
> Picture #1 shows a dump when my laptop crashed (before reboot).
> btrfs no csum found for inode X start Y
> http://marc.merlins.org/tmp/crash.jpg
> 
> Mounting with 3.5.0 and 3.6.3 gives the same error:
> 
> gandalfthegreat:~# mount -o recovery,skip_balance,ro /dev/mapper/bootdsk                                  
> 
> shows
> btrfs: bdev /dev/mapper/bootdsk errs: wr 0, rd 0, flush 0, corrupt 1, gen 0
> btrfs: bdev /dev/mapper/bootdsk errs: wr 0, rd 0, flush 0, corrupt 2, gen 0
> (there are 2 lines, not sure why)
> 
> kernel BUG at fs/btrfs/volumes.c:3707
> int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
> {
> 	struct extent_map *em;
> 	struct map_lookup *map;
> 	struct extent_map_tree *em_tree = &map_tree->map_tree;
> 	int ret;
> 
> 	read_lock(&em_tree->lock);
> 	em = lookup_extent_mapping(em_tree, logical, len);
> 	read_unlock(&em_tree->lock);
> 	BUG_ON(!em);  <---
> 
> If the snapshot helps (sorry, hard to read, but usable):
> http://marc.merlins.org/tmp/btrfs_bug.jpg
> 
> Questions:
> 1) Any better way to get a proper dump without serial console?
> (I hate to give you pictures)
> 
> 2) Should I try btrfsck now, or are there other mount options than
> mount -o recovery,skip_balance,ro /dev/mapper/bootdsk 
> I should try?
> 
> 3) Want me to try btrfsck although it may make it impossible for me to
> reproduce the bug and test a fix, as well as potentially break the filesystem
> more (last time I tried btrfsck, it outputted thousands of lines and never converged
> to a state it was happy with)
> 
> Thanks,
> 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/  
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-- 
"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/