Comment 2 for bug 791992

I noticed 'rsyslogd' was doing an awful lot of work, and when checking /var/log/syslog I found lots of btrfs output when rsyncing (for backup):

------------[ cut here ]------------
WARNING: at /build/buildd/linux-2.6.35/fs/btrfs/extent-tree.c:3441 btrfs_block_rsv_check+0x1c3/0x220 [btrfs]()
Hardware name: P4SCE
Modules linked in: aes_i586 aes_generic ip6table_filter ip6_tables ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT iptable_mangle xt_tcpudp iptable_filter sha256_generic ip_tables x_tables blowfish bridge stp dm_crypt ppdev parport_pc lp shpchp parport raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor xor async_memcpy async_tx raid1 raid0 multipath linear btrfs zlib_deflate crc32c libcrc32c intel_agp e1000 agpgart floppy
Pid: 1731, comm: rsync Not tainted 2.6.35-28-generic-pae #50-Ubuntu
Call Trace:
 [<c0152b92>] warn_slowpath_common+0x72/0xa0
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<c0152be2>] warn_slowpath_null+0x22/0x30
 [<f888b8e3>] btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f889f66c>] __btrfs_end_transaction+0x17c/0x1f0 [btrfs]
 [<f889f70f>] btrfs_end_transaction+0xf/0x20 [btrfs]
 [<f889f926>] start_transaction+0x206/0x210 [btrfs]
 [<f889f98c>] btrfs_start_transaction+0x1c/0x20 [btrfs]
 [<f88a07e8>] __unlink_start_trans+0x38/0x410 [btrfs]
 [<c023b1af>] ? mntput_no_expire+0x1f/0xd0
 [<f88a67f3>] btrfs_unlink+0x33/0x110 [btrfs]
 [<c022c5ee>] ? inode_permission+0x9e/0xb0
 [<c022d757>] vfs_unlink+0x87/0xd0
 [<c022f2e7>] do_unlinkat+0x157/0x180
 [<c02237b5>] ? vfs_read+0x125/0x190
 [<c0223862>] ? sys_read+0x42/0x70
 [<c022f325>] sys_unlink+0x15/0x20
 [<c05f1f04>] syscall_call+0x7/0xb
---[ end trace d4686b8f4d931797 ]---
block_rsv size 788529152 reserved 321339392 freed 0 0
------------[ cut here ]------------
WARNING: at /build/buildd/linux-2.6.35/fs/btrfs/extent-tree.c:3441 btrfs_block_rsv_check+0x1c3/0x220 [btrfs]()
Hardware name: P4SCE
Modules linked in: aes_i586 aes_generic ip6table_filter ip6_tables ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT iptable_mangle xt_tcpudp iptable_filter sha256_generic ip_tables x_tables blowfish bridge stp dm_crypt ppdev parport_pc lp shpchp parport raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor xor async_memcpy async_tx raid1 raid0 multipath linear btrfs zlib_deflate crc32c libcrc32c intel_agp e1000 agpgart floppy
Pid: 1731, comm: rsync Tainted: G W 2.6.35-28-generic-pae #50-Ubuntu
Call Trace:
 [<c0152b92>] warn_slowpath_common+0x72/0xa0
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<c0152be2>] warn_slowpath_null+0x22/0x30
 [<f888b8e3>] btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f887f6d0>] ? btrfs_free_path+0x20/0x30 [btrfs]
 [<f88d0359>] ? btrfs_insert_orphan_item+0x79/0x90 [btrfs]
 [<f889f66c>] __btrfs_end_transaction+0x17c/0x1f0 [btrfs]
 [<f889f6f2>] btrfs_end_transaction_throttle+0x12/0x20 [btrfs]
 [<f88a6879>] btrfs_unlink+0xb9/0x110 [btrfs]
 [<c022d757>] vfs_unlink+0x87/0xd0
 [<c022f2e7>] do_unlinkat+0x157/0x180
 [<c02237b5>] ? vfs_read+0x125/0x190
 [<c0223862>] ? sys_read+0x42/0x70
 [<c022f325>] sys_unlink+0x15/0x20
 [<c05f1f04>] syscall_call+0x7/0xb
---[ end trace d4686b8f4d931798 ]---
block_rsv size 788529152 reserved 320417792 freed 61440 462848
------------[ cut here ]------------
WARNING: at /build/buildd/linux-2.6.35/fs/btrfs/extent-tree.c:3441 btrfs_block_rsv_check+0x1c3/0x220 [btrfs]()
Hardware name: P4SCE
Modules linked in: aes_i586 aes_generic ip6table_filter ip6_tables ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT iptable_mangle xt_tcpudp iptable_filter sha256_generic ip_tables x_tables blowfish bridge stp dm_crypt ppdev parport_pc lp shpchp parport raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor xor async_memcpy async_tx raid1 raid0 multipath linear btrfs zlib_deflate crc32c libcrc32c intel_agp e1000 agpgart floppy
Pid: 1626, comm: btrfs-transacti Tainted: G W 2.6.35-28-generic-pae #50-Ubuntu
Call Trace:
 [<c0152b92>] warn_slowpath_common+0x72/0xa0
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f888b8e3>] ? btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<c0152be2>] warn_slowpath_null+0x22/0x30
 [<f888b8e3>] btrfs_block_rsv_check+0x1c3/0x220 [btrfs]
 [<f88da923>] ? btrfs_find_ref_cluster+0x63/0x1a0 [btrfs]
 [<f889f66c>] __btrfs_end_transaction+0x17c/0x1f0 [btrfs]
 [<f889f70f>] btrfs_end_transaction+0xf/0x20 [btrfs]
 [<f889f40c>] btrfs_commit_transaction+0x59c/0x680 [btrfs]
 [<f889f8b0>] ? start_transaction+0x190/0x210 [btrfs]
 [<c016e610>] ? autoremove_wake_function+0x0/0x50
 [<f8899d67>] transaction_kthread+0x217/0x230 [btrfs]
 [<f8899b50>] ? transaction_kthread+0x0/0x230 [btrfs]
 [<c016e1e4>] kthread+0x74/0x80
 [<c016e170>] ? kthread+0x0/0x80
 [<c010997e>] kernel_thread_helper+0x6/0x10
---[ end trace d4686b8f4d931799 ]---
block_rsv size 788529152 reserved 320663552 freed 278528 0

etc. etc. (after this it seems to go between "rsync Tainted" and "btrfs-transacti Tainted")

I'm running 'btrfsck' now...