abrt version: 2.0.3
architecture:   x86_64
cmdline:        ro root=/dev/mapper/vg_fdiegz-lv_root rd_LVM_LV=vg_fdiegz/lv_root rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=es_ES.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=es rhgb quiet
component:      kernel
kernel:         2.6.38.8-35.fc15.x86_64
kernel_tainted: 512
kernel_tainted_long: Taint on warning.
os_release:     Fedora release 15 (Lovelock)
package:        kernel
reason:         WARNING: at fs/btrfs/disk-io.c:381 __btree_submit_bio_start+0x124/0x1aa [btrfs]()
time:           Wed Jul 27 19:16:28 2011

backtrace:
:WARNING: at fs/btrfs/disk-io.c:381 __btree_submit_bio_start+0x124/0x1aa [btrfs]()
:Hardware name: K52Jr
:Modules linked in: tun fuse usb_storage uas sco bnep l2cap bluetooth ebtable_nat ebtables ipt_MASQUERADE iptable_nat nf_nat xt_CHECKSUM iptable_mangle bridge stp llc sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables arc4 snd_hda_codec_hdmi snd_hda_codec_conexant ath9k snd_hda_intel snd_hda_codec mac80211 snd_hwdep snd_seq snd_seq_device jmb38x_ms ath9k_common ath9k_hw uvcvideo ath iTCO_wdt microcode videodev joydev snd_pcm intel_ips memstick serio_raw v4l2_compat_ioctl32 iTCO_vendor_support cfg80211 jme snd_timer i2c_i801 mii snd soundcore snd_page_alloc asus_laptop sparse_keymap rfkill virtio_net kvm_intel kvm ipv6 btrfs zlib_deflate libcrc32c sdhci_pci sdhci mmc_core video radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core [last unloaded: scsi_wait_scan]
:Pid: 4945, comm: btrfs-worker-2 Not tainted 2.6.38.8-35.fc15.x86_64 #1
:Call Trace:
: [<ffffffff8105511a>] warn_slowpath_common+0x83/0x9b
: [<ffffffff8105514c>] warn_slowpath_null+0x1a/0x1c
: [<ffffffffa018f3ea>] __btree_submit_bio_start+0x124/0x1aa [btrfs]
: [<ffffffffa018de8c>] run_one_async_start+0x25/0x27 [btrfs]
: [<ffffffffa01b7dfb>] worker_loop+0x145/0x46e [btrfs]
: [<ffffffffa01b7cb6>] ? worker_loop+0x0/0x46e [btrfs]
: [<ffffffff8106ebaf>] kthread+0x84/0x8c
: [<ffffffff8100a9e4>] kernel_thread_helper+0x4/0x10
: [<ffffffff8106eb2b>] ? kthread+0x0/0x8c
: [<ffffffff8100a9e0>] ? kernel_thread_helper+0x0/0x10

comment:
:I'm working with LibreOffice Calc, and Ubuntu Server virtualized with KVM.
:The machine it was slow.