Re: btrfs hang on nfs?

["Scott E. Blomquist" <sb@techsquare.com>]

Nikolay Borisov writes:
 > 
 > On 14.01.19 г. 13:42 ч., Scott E. Blomquist wrote:
 > > 
 <snip>
 > > 
 > > The file system hung again below is the sysrq output
 > > 
 > > Linux kanlabfs 4.19.13-custom #1 SMP Wed Jan 9 08:36:50 EST 2019 x86_64 x86_64 x86_64 GNU/Linux
 > > 
 > > btrfs-progs v4.19.1 
 > > 
 > > # btrfs fi df /export/
 > > Data, single: total=79.61TiB, used=79.61TiB
 > > System, single: total=36.00MiB, used=8.31MiB
 > > Metadata, single: total=192.01GiB, used=190.19GiB
 > > GlobalReserve, single: total=512.00MiB, used=0.00B
 > 
 > So this btrfs is hosted on your local machine but it is exported via
 > NFS, correct?

Correct and via samba also

 > > 
 > > #  btrfs fi show
 > > Label: '/export'  uuid: 8f92c2e4-86fe-48cb-b2d3-bc36da765f02
 > >         Total devices 3 FS bytes used 79.79TiB
 > >         devid    1 size 47.30TiB used 43.58TiB path /dev/sda1
 > >         devid    2 size 21.83TiB used 18.11TiB path /dev/sdb1
 > >         devid    3 size 21.83TiB used 18.11TiB path /dev/sdc1
 > 
 > What kind of disks are those, presumably spinning rust due to their size
 > but what model/make?
 > 

3 x raid 6 on a LSI MegaRAID SAS 9271-8i

 > > [Mon Jan 14 06:24:26 2019] sysrq: SysRq : Show Blocked State
 > 
 > <snip>
 > 
 > > [Mon Jan 14 06:24:26 2019] btrfs-transacti D    0  6808      2 0x80000000
 > > [Mon Jan 14 06:24:26 2019] Call Trace:
 > > [Mon Jan 14 06:24:26 2019]  ? __schedule+0x2ea/0x870
 > > [Mon Jan 14 06:24:26 2019]  schedule+0x32/0x80
 > > [Mon Jan 14 06:24:26 2019]  btrfs_start_ordered_extent+0xca/0x100 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  ? wait_woken+0x80/0x80
 > > [Mon Jan 14 06:24:26 2019]  btrfs_wait_ordered_range+0xbd/0x110 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  __btrfs_wait_cache_io+0x49/0x1a0 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  btrfs_write_dirty_block_groups+0xed/0x360 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  ? btrfs_run_delayed_refs+0x8b/0x1d0 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  commit_cowonly_roots+0x1ed/0x280 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  btrfs_commit_transaction+0x36e/0x8d0 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  ? start_transaction+0x9b/0x3f0 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  transaction_kthread+0x14d/0x180 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  kthread+0xf8/0x130
 > > [Mon Jan 14 06:24:26 2019]  ? btrfs_cleanup_transaction+0x530/0x530 [btrfs]
 > > [Mon Jan 14 06:24:26 2019]  ? kthread_bind+0x10/0x10
 > > [Mon Jan 14 06:24:26 2019]  ret_from_fork+0x35/0x40
 > 
 > So the transaction is being committed as a result of that
 > btrfs_start_ordered_extent, which flushes data to disk. Since you've
 > compiled your kernel can you run the following command from the kernel's
 > source:
 > 
 > ./scripts/faddr2line  vmlinux  btrfs_start_ordered_extent+0xca/0x100
 > 
 > 'vmlinux' should be the kernel executable with debug info that results
 > from compiling the kernel. I want to figure out which line exactly
 > btrfs_start_ordered_extent+0xca/0x100 resolves to.

 <snip>

I'll have to rebuild the kernel with debug symbols.  Do I have to be
booted into the kernel for that command to be useful?

Cheers and Thanks,

sb. Scott Blomquist